ITfl 681 
.P8 

Copy 1 



Manual 

Training Course 

in Concrete 



CONCRETE FOR 
PERMANENCE 



PUBLISHED BY 

Association of 

American Portland Cement 

Manufacturers 

Bellevue Court Building 
Philadelphia, Pa* 

1915 



Lessons and General Outline 
With Suggested Exercises 

FOR A 

Manual Training Course 
in Concrete 

PREPARED FOR THE USE OF INSTRUCTORS 

IN PLANNING AND CONDUCTING ELEMENTARY 

WORK IN CONCRETE 




Price, 25 Cents per Copy 



XAsOCC- 



a* 



PUBLISHED BY 

Association of American Portland Cement 

Manufacturers 

Bellevue Court Building, Philadelphia, Pa. 

1915 

Copyrighted, 191 5, by the Association of American Portland Cement Manufacturers 



Preface 

Concrete is so extensively used as a material of construction as to make 
the need for a short general course in elementary and high schools impera- 
tive. This has warranted the preparation of a series of elementary lessons 
and exercises which may be used to stimulate the interest and ingenuity of 
the younger students, thus widening, at a formative period, their knowledge 
of cement and the materials used in concrete construction. 

The scope of this course is necessarily limited by the time available for 
presenting such a subject. The Association of American Portland Cement 
Manufacturers has prepared, from time to time, various bulletins treating 
of the application of concrete in countless ways, and the instructor may 
readily enlarge or vary the course by using these bulletins as text-books or 
guides in the preparation of more extended lectures or problems. 

For reference purposes the name, number, and general scope of the 
bulletins are given below: 

Concrete Surface Finish. 

Reinforced Concrete Chimneys. 

Cement Stucco. 

Concrete Tanks. 

Concrete in the Country. 

Factories and Warehouses of Concrete. 

The Concrete House and Its Construction. 

Concrete Highways. 

Facts Everyone Should Know About Concrete Roads. 

Standard Methods of Testing and Specifications for Cement. 

Lessons, General Outline, and Suggested Exercises for a Manual 

Training Course in Concrete. 
Concreting in Winter. 
Short-span Concrete Bridges. 
Single Track Streets and Dished Alleys. 
A Concrete Country Road. 
Maintenance of Concrete RQads and Streets. 
Standard Recommended Practice in Concrete Road Construction. 
Concrete School Houses. 
Concrete Silos. 
Concrete Blocks. 
Concrete Drain Tile. 
Concrete Pipe. 

The files of the leading technical papers are replete with articles dealing 
with the use of cement and concrete for specific purposes. The Proceed- 
ings of the American Concrete Institute (Philadelphia) also contain much 
valuable information. Instructors and students may very readily increase 
their working knowledge of any phase of concrete construction by consult- 
ing these papers and proceedings. ^ 

^©C1,A398810 

MAY 12 1915 



No. 


10. 


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18. 


No. 


22. 


No. 


23. 


No. 


26. 




Table of Contents 

LESSONS 

I. Manufacture of Portland Cement 5 

II. Concrete Aggregates 11 

III. Proportioning, Mixing and Placing of Concrete 20 

IV. Forms 28 

V. Concrete Foundations and Walls 33 

VI. The Surface Finish of Concrete 41 

VII. Cement Products 47 

VIII.* Concrete Walks and Curbs 54 

LABORATORY GUIDE 

General Notes 64 

Equipment Required 66 

I. Materials and Mixtures 67 

II. Forms and Molds 71 

Plate 1 . — Assembled Form for Concrete Test Specimens 72 

Plate 2. — Detail of Form for Test Specimens 74 

Plate 3. — Assembled Form for Concrete Test Specimens 75 

III. Tools and Equipment 76 

Plate 4. — Device for Testing Small Concrete Specimens 77 

Plate 5. — Cement Testing Machine 79 

Plate 6. — Details of Cement Testing Machine 80 

IV. Walk and Floor Work 78 

Plate 7. — Details of Concrete Horseblock Form 81 

Plate 8. — Details of Concrete Step and Porch Construction 83 

Plate 9. — Details of Cement Sidewalk Construction 84 

V. Elementary Theory of Reinforcement 85 

VI. Unit Construction 86 

Plate 10. — Design of Concrete Pedestals 87 

Plate 11.— Concrete Bird Bath 88 

Plate 12.— Simple Garden Bench 89 

VII. Posts and Columns 90 

VIII. Foundations and Piers 91 

IX. Ornamental Work 92 

Plate 13. — Design for Concrete Urns 95 

Plate 14. — Concrete Flower Boxes 96 

Plate 15. — Details of Concrete Trough Construction 97 

Plate 16. — Small Concrete Watering Trough 98 

Plate 17.— Concrete Hotbed 99 



I. Manufacture of Portland Cement 

Cements and limes have been used since the dawn of civilization. The 
famous Appian Way, the great system of aqueducts and other structures 
built by the Romans, are to-day in a remarkable state of preservation, and 
proof positive that they understood the use of cement and concrete. 

Notwithstanding the early use of these materials, little was known of 
their chemistry, and no substantial advance was made in the manufacture 
of lime and cement from the time of the Romans until 1756, when John 
Smeaton, who had been employed by the English government to build a 
lighthouse upon a group of gneiss rocks in the English Channel, near the 
coast of Cornwall in Devonshire, discovered that an impure or clayey lime- 
stone, when burned and slaked, would harden into a solid mass under water, 
as well as in air. This discovery of Smeaton' s seemed to pave the way for 
rapid improvement and development in the lime and cement industries. 
In 1796 James Parker, of Northfleet, England, obtained a patent for the 
manufacture of a cement which he aptly named Roman cement. Parker's 
process consisted of burning certain stone or argillaceous products called 
" nodules of clay" in an ordinary lime kiln, and then grinding to a powder. 
Cement produced in this manner rapidly gained favor among engineers and 
builders, and resulted in natural cement plants springing up all over the 
continent of Europe, England, and later, about 1818, in the United States. 
In 1824 Joseph Aspdin took out a patent in England for the manufacture of 
an improved cement, produced by calcining a mixture of limestone and clay. 
To the resulting powder he gave the name of "Portland Cement," because, 
when it hardened, a yellowish-gray mass was produced, resembling in 
appearance the stone found in various quarries on the isle of Portland off 
the south coast of England. To Joseph Aspdin, therefore, is given the 
credit of making the first Portland cement, and he is generally recognized as 
the father of the modern Portland cement industry. 

In this country the cement industry began with the discovery, in 1818, 
of a natural cement rock near Chittenango, Madison County, New York, 
by Canvass White, an engineer on the Erie Canal. In 1825 cement rock 
was found in Ulster County, New York, along the Delaware and Hudson, 
and in 1828 a mill was built in Rosendale, New York, and it was from this 
place that the natural cement obtained its name. Other canals along which 

5 



cement rock was discovered, with location and date, are : Illinois & Michi- 
gan Canal, at Utica, 111., in 1838; James River Canal at Balcony Falls, Va., 
in 1848; and Lehigh Coal & Navigation Co. Canal at Siegfried, Penna., in 
1850. 

In the spring of 1866 D. O. Saylor, Esaias Rehrig, and Adam Woolever, 
all of Allentown, Penna., formed the Coplay Cement Co. and located near 
Allentown. Mr. Saylor was president and superintendent of the mill. 
Early in the seventies he began experimenting on Portland cement from the 
rock in the quarries. Noticing that although the harder burned portions of 
his Rosendale clinker gave a cement which in a short period of time would 
show tensile strength equal to the best European Portland cement, it soon 
crumbled away. He decided that this was because the raw material was 
not properly proportioned. The result of these experiments taught him to 
mix his high-limed cement rock and low-limed cement rock in the correct 
proportions, and after many experiments and trials true Portland cement 
was produced in 1875. This was the first Portland cement made in the 
Lehigh district and probably in the United States. 

Knowing how to produce a high-grade Portland cement was not all 
that was necessary. The next difficulty encountered was the sale of it. 
This new American Portland cement was manufactured at a high cost; 
therefore it could not be offered at a lower price than the imported article, 
and it was only by aggressive methods that Mr. Saylor secured a market for 
his product, which amounted to only 1700 barrels a year. 

About the same time Thomas Millen was constructing a plant at South 
Bend, Ind., and plans were soon under way at Wampum, Penna., Kala- 
mazoo, Mich., and Rockford, Me., for other mills. 

This, then, was the small beginning of the American Portland cement 
industry, which has grown from a production of about 83,000 barrels in 
1880, and less than 1,000,000 in 1895, to the total of approximately 92,000,- 
000 in 1913. 

This brief history of the development of the industry prompts the ques- 
tion, "Just what is Portland cement?" This is probably answered by the 
definition given in the "Standard Specifications for Portland Cement" 
adopted by the American Society for Testing Materials. This definition is 
quite formidable, consisting, as it does, of long phrases and equally long 
words, and, in order to be understood, will undoubtedly require some 
explanation. 

"Portland cement is the term applied to the finely pulverized product 
resulting from the calcination to incipient fusion of an intimate mixture of 
properly proportioned argillaceous and calcareous materials, and to which 
no addition greater than 3 per cent, has been made subsequent to calcina- 
tion." 

6 



This definition gives, in addition to the composition, an outline of the 
process of manufacture, but not in the order taken in manufacture. These 
several points in their natural order would be as follows : 

First — that Portland cement is composed of calcareous and argillaceous 
materials. 

Second — that the raw materials must be properly selected and prepared 
for the process of manufacture, due regard being given to proper proportion- 
ing. 

Third — that there must be an intimate mixture of the raw materials. 
This necessitates the drying, fine grinding, and thorough mixing of the raw 
materials. 

Fourth — that the raw material or mixture must be burned to a clinker and 
that the heat must be such as to cause a partial melting of the ingredients. 

Fifth — that the finished product, or Portland cement, is the product 
obtained by grinding this clinker to a powder. 

The last clause in the definition provides for the addition of a small 
amount of some material to regulate the setting time, but limits the quan- 
tity to prevent adulteration. 

The principal elements or compounds in Portland cement are lime 
(CaO), silica (Si0 2 ), and alumina (A1 2 3 ), but a small percentage of oxide of 
iron (Fe 2 03) and magnesia (MgO) is also contained. 

The composition of a standard Portland cement is usually within the 
following limits : 

Compounds Per Cent. Limits 

Silica (Si0 2 ) 20 to 24 

Alumina (A1 2 3 ) 5 to 10 

Iron oxide (Fe 2 3 ) 2 to 5 

Lime (CaO) 60 to 65 

Magnesia (MgO) „ . 1 to 4 

Sulphur trioxide (S0 3 ) 0.5 to 1.75 

Nature has provided an abundance of these calcareous and argillaceous 
materials suitable for the manufacture of Portland cement. The calcare- 
ous variety is always in the form of calcium carbonate, such as limestone, 
chalk, marl, or the precipitated form obtained as a waste-product from the 
manufacture of alkalis. The argillaceous division includes clay, shale and 
slate, cement rock, and selected blast furnace slag. Cement is made in this 
country from all these materials, each plant using one of the calcareous 
combined with one of the argillaceous materials. 

Portland cement may also be divided into classes, according to the 
method of manufacture, which are as follows: 

1. Wet process. 

2. Semi-wet process. 

3. Dry process. 

7 



In the wet process the raw materials are intimately mixed, ground, and 
fed (in the form of a slurry containing sufficient water to make it of a fluid 
consistence) into the rotary kilns. In the semi-wet process a similar but 
drier slurry is used, while in the dry process raw materials are ground, 
mixed, and burned in the dry state. 

Because of the fact that the larger portion of Portland cement manu- 
factured in the United States to-day is made by plants using the dry proc- 
ess, the description of the process of manufacture will be confined to an 
account of this method. 

The manufacture of Portland cement itself is divided into five heads, 
as follows : 

1. Mining and quarrying of raw materials. 

2. Drying and grinding. 

3. Proportioning and mixing. 

4. Burning the mixed materials to incipient fusion. 

5. Grinding the clinker thus burned to an extremely fine powder, mean- 
while adding the proper proportion of gypsum, the resulting powder being 
known as Portland cement. 

The excavation of the raw materials is the first step toward the actual 
manufacture of Portland cement, and the one concerning which least has 
been published. Local conditions enter into this preliminary stage to such 
an extent that few general statements can be made concerning it. The 
natural raw materials are worked by one of three general methods. First, 
quarrying and digging from open pits. Second, mining from underground 
workings. Third, dredging from deposits covered by water. Inasmuch 
as this paper deals with the manufacture of Portland cement itself, we will 
not go deeply into the preparation of the raw material. 

The raw materials for the greater part of the Portland cement made in 
the United States to-day are : 

(a) Limestone and clay, shale or slag. 

(b) Cement rock and pure limestone. 

The method of quarrying the rocks usually follows that customary in all 
quarry operations. The rock is dislodged from the quarry face by means of 
an explosive and then loaded into side dump cars or aerial trams by either 
steam shovel or manual labor, preferably the former. The stone is then 
conveyed to the stone house, where it is crushed to comparatively small 
sizes and then transported to storage-bins before being mixed with the 
other ingredients. While in storage the stone may be sampled and ana- 
lyzed. Another method used is to pass the limestone, shale, or cement rock 
through crushers and ball mills, or other preliminary grinders, from which 
it is conveyed to storage-bins. The ball mills are cylindrical steel drums 
containing a quantity of steel balls. The material to be ground, after dry- 

8 



ing, is continuously added. As the cylinder rotates the balls roll, thus 
grinding the rocks to coarse grits. The coarse grits are then run into stor- 
age-bins. Tube mills which are used further on in the process are similar 
in general to the ball mills. 

Shale, which for practical purposes may be looked upon as solidified 
clay, is excavated, dried, ground, and then conveyed to storage-bins. 

After the raw materials have been drawn from their respective bins and 
accurately proportioned by weighing, they are delivered to a screw con- 
veyor which completes the mixing and delivers the combined material to 
the tube mills. The tube mills are revolving cylinders half full of flint 
pebbles or steel slugs which reduce the material continually being fed 
into practically the fineness of finished cement. At this point, however, 
we are a long way from the finished cement, since the product of these 
mills has a long journey before it is ready for the consumer. 

All the tube mills deliver to the same conveyor, which results in a uni- 
form product of the raw material mill as a whole. At frequent intervals 
samples are taken from the belt and delivered to a sample can which is 
collected at stated intervals by one of the chemist's assistants. The sample 
is then taken to the laboratory where tests are made to determine its 
composition. 

From the tube mills the material is fed to the kilns through a system of 
conveyors. The kilns themselves are from 6 to 8 feet in diameter and 
from 60 to 150 feet long, 125 feet being the average length. They are 
lined with fire brick and revolve at about the rate of one revolution per 
minute. It is estimated that a particle of raw material takes about an 
hour to traverse the entire distance from the feed to the outlet. Powdered 
bituminous coal, crude oil, or gas is used as fuel, powdered coal being 
the one most generally used. It is blown into the kiln at the end opposite 
that at which the raw materials enter. 

The raw material entering as a powder is gradually brought to the point 
of incipient fusion at a temperature of 2500° to 3000° Fahrenheit, producing 
clinkers varying in size from J4 mcn U P to about 1 J^ inches in diameter. It 
may also be mentioned that the clinker is red hot when discharged, but is 
soon cooled by sprays of water or cold-air blasts which are played over the 
elevator and also upon the clinker when delivered to the storage piles. 

If we go to the front of the kilns, we will see that the method of heating 
is the same as used in drying slag and limestone, with the difference that 
considerably more fuel and blast are required as a higher temperature is 
necessary. By means of smoked glasses experienced workmen are able at 
all times to note the condition within the kiln. 

From the kiln, the clinker may go — (a) to the clinker storage pile for 
later grinding, or (6) directly to the grinding department. 

Either before or after the preliminary grinding of the clinker by jaw 

9 



crusher it is usual to add gypsum, either by hand or automatically, in 
order to retard the setting time of the cement. Were gypsum not added, 
the cement would harden quickly and develop little strength. Approxi- 
mately two pounds of gypsum are added to every 100 pounds of clinker. 
This is controlled by the chemist from analyses of the finished cement and 
from the setting determinations made hourly in the physical laboratory. 

After the gypsum has been added, the material is delivered to the tube 
mills, which complete the grinding. These tube mills are similar to those 
which grind the raw material, and are also half full of flint pebbles or steel 
slugs which rotate and grind one against the other, reducing the cement to 
the fineness with which every one is familiar. There are also special, grind- 
ing machines which supplement the tube mills. Frequent samples are 
taken of the finished product. It is customary to make up test pats every 
hour and briquettes twice a day, while in the chemical laboratory complete 
analyses are continually being made of the finished product, as well as of 
the raw materials which enter into its composition. 

The bins used for storage are similar to those used in storing grain. The 
material is deposited in these bins by means of a conveyor belt with a trip- 
ping mechanism which can be run from one end of the house to the other. 
The cement is drawn out from below through holes in the floor, delivering to 
screw conveyors underneath. A peculiarity noted in drawing cement or 
other similar material is that when the drawing is started, the cement comes 
out as an average of the entire bin. If, for example, only one hole is opened 
below the bin, the top surface will "cave" slightly after the drawing is con- 
tinued for a short time, and from then on small portions are observed to 
fold in from the outside of the crater, indicating that an average of the entire 
stock is being delivered below. From each of the tunnels conveyors carry 
the cement to large elevators, which raise it finally to large hoppers above 
the packing floor, on which are installed packing machines. A cement 
sack may be filled (when packing machines are used) through the bottom, 
and not through the top. The bags are tied previous to filling, and a 
valve may be discovered by careful inspection of any of the standard sacks 
used to-day. Every modern cement manufacturer employs a packing 
machine for filling sacks. As sacks are filled a conveyor belt running the 
entire length of the packing room unloads them within a few feet of the 
car, ready for shipment. 

REFERENCES 

"Portland Cement," by Richard R. Meade. Published by The Chemical Publishing 

Co., Easton, Pa. 
"Materials of Construction," by J. B. Johnson. Published by John Wiley & Sons, 

New York City. 

10 



II. Concrete Aggregates 

Present-day success in the use of concrete is not due to any particular 
" discovery," but is the result of a consistent, scientific study and investiga- 
tion of the component materials. 

As ordinarily employed, the term " aggregates" includes not only gravel 
or stone, the coarse material used, but also the sand, or fine material, mixed 
with the cement to form either mortar or concrete. Fine aggregate is 
defined as any suitable material that will pass a No. 4 sieve or screen having 
four meshes to the linear inch, and includes sand, stone screenings, crushed 
slag, etc. By coarse aggregate is meant any suitable material, such as 
crushed stone and gravel, that is retained on a No. 4 sieve. The maximum 
size of coarse aggregate depends on the class of structure for which the con- 
crete is to be used. 

The strength of concrete can never be greater than that of the materials 
used as aggregates. Nothing is more conducive to unsatisfactory results in 
concrete work than poor aggregates. The condition of the cement, methods 
of mixing, the proportions used, and the amount of water added, also the 
method of depositing and curing concrete, all have their effect upon its 
density and strength, but even with the most careful attention given to 
these details, good results are impossible without good aggregates. 

The fact that the aggregates seem of good quality yet may be proved 
totally unsuitable shows that study and careful tests are necessary if the best 
results are to be obtained. The idea that the strength of concrete depends 
entirely upon the cement and that only a superficial examination of aggre- 
gates is necessary, is altogether too prevalent. The man who understands 
his aggregates, grades them properly, sees that they are washed, if neces- 
sary, then mixes them in proportions determined by thorough testing, study, 
or actual experiences, is the one who will make the best concrete. 

In the selection and use of sand more precautions are necessary than 
for the coarser aggregate, due to its physical condition and a wider variation 
in properties. A knowledge of these properties and of the method of analy- 
sis to determine the suitability of sand for use in mortar and concrete may 
be easily applied to an analysis of the coarse aggregate. (Stone screenings, 
broken stone, and gravel will be discussed only where their properties and 
the methods of examining them differ from those of sand.) 

11 



Origin and Composition 

Geologists classify rook in one of two large groups: 

1. Igneous. 

2. Sedimentary. 

Igneous Rocks 

Igneous rocks are those which have been formed by the cooling of fused 
material. They are classified either as massive or laminated, according to 
their structure. The massive igneous rocks are those which have been 
solidified, undisturbed, from a fused state, and which have not been subse- 
quently subjected to severe external stresses. When the rock was sub- 
jected, either during or after cooling, to external pressure, a laminated 
structure seems to have resulted, with the component minerals arranged 
in more or less definite alternating bands. Most granites and all trap-rock 
belong to the first class, while rocks of the second class are termed gneisses. 

Sedimentary Rocks 

Sedimentary rocks are those derived from the breaking up or disinte- 
gration of preexisting strata, the material so obtained being carried, usually 
in suspension or solution, to some point where it is redeposited as a bed of 
fine particles, clay, or calcareous material, such as shells, marls, etc. Sub- 
sequently, this loosely deposited material may become consolidated and 
compacted by pressure or other agencies, the result being the formation of 
sandstone, shale and slate, or limestones, dolomites, and marbles. 

Sedimentary rocks may be classified on a combined chemical and physical 
basis, distinguished by the material of which they are chiefly composed, as : 

1. Silicious sedimentary or sandstone and conglomerates. 

2. Argillaceous or clayey rocks, such as shales and slates. 

3. Calcareous rocks, namely, marble, compact limestone, granular 

limestone, and magnesian limestone, or dolomites. 

Sources of Supply 

The materials commonly used as coarse concrete aggregate in different 
places throughout the United States are the sedimentary rocks, which may 
be grouped into three classes on the basis of origin : 

1. Glacial deposits. 

2. Coastal plain deposits. 

3. Stream deposits. 

All these deposits contain more or less silt, clay, loam, or other finely 
divided impurities. 

The gravel beds of the glacial drifts furnish excellent material for con- 

12 



crete. Baker, in "Roads and Pavements," says: "Glacial gravel exists in 
considerable quantities in western Pennsylvania, in the greater part of 
Ohio, in northern Indiana, and in Illinois, and to some extent in several of 
the States of the southwest. There are large areas of this gravel in Wiscon- 
sin, Minnesota, and Iowa." 

Physical Conditions 

Sands differ not only in chemical and mineralogic composition, but in 
physical condition. They often contain many impurities, and the methods 
for determining their presence, as well as their effects, should be known. 

Impurities 

Many of these impurities impair the hardening properties of cement, 
and hence the strength of the concrete in which used. Much has been 
written relative to the effect of clay upon concrete, and many contradictory 
opinions have been advanced. Engineers are, however, fairly in accord on 
certain conclusions. When clay exists as a coating on the particles of sand 
aggregate, it is undoubtedly injurious, as proper adhesion between the 
cement and the sand surfaces is then prevented. When, however, clay of a 
silicious nature in the form of separate particles exists to a small extent 
throughout the mass of aggregate, it appears to cause no serious harm in 
many kinds of concrete work. Clay in this form acts as an adulterant, 
without seriously reducing the tensile strength of the concrete. Their 
opinions, however, are based largely on the results of tensile-strength tests 
on relatively dry mixtures. It is doubtful whether, under field conditions, 
or even in large compression-test specimens made up in the laboratory, 
these results would be obtained. An excess of clay tends to lead one into 
believing that the concrete contains an excess of cement rather than a 
shortage. The only advantage that can be claimed for the presence of clay 
is that it increases the density of the concrete by filling some of the voids. 

The presence of clay in sand may be detected by the well-known method 
of rubbing the material between the hands. If clean, the sand should not 
adhere to or discolor the hands. Also a small quantity of the sand may be 
stirred or shaken in a tumbler or bottle of water, when the presence of clay 
will at once be shown by a characteristic cloudiness of the water. Since the 
clay remains longer in suspension than the sand, it will separate and settle 
later in a layer on top. 

Vegetable Matter 

A coating of vegetable matter on sand grains appears not only to prevent 
the cement from adhering, but to affect it chemically. Frequently a quan- 
tity of vegetable matter so small that it cannot be detected by the eye, and 

13 



only slightly disclosed in chemical tests, may prevent the mortar from reach- 
ing any appreciable strength. Concrete made with such sand usually 
hardens so slowly that the results are questionable and its use is prohibited. 
Other impurities, such as acids, alkalis, or oils in the sand or mixing water, 
usually make trouble. 

The usual way of determining the quality of sand is to make up bri- 
quettes in the proportions of one part cement to three parts of the sand to 
be tested, and compare the results with the strength of a mortar made with 
the same cement and standard Ottawa sand in like proportions and of 
standard consistence. Standard Ottawa sand is exceptionally uniform, and 
is obtained from Ottawa, 111. 

The presence of moisture in sand may make proper mixing with other 
materials somewhat difficult, as a uniform distribution of cement in the 
mortar is hard to obtain. 

General Requirements 

The quality of concrete is affected by — 

1. The hardness, or crushing strength, of the aggregates. 

2. Their durability or resistance to weather and abrasion. 

3. Grading, or maximum and relative sizes, of particles. 

4. Cleanliness or freedom from foreign materials. 

5. The shape and nature of the surface of the particles. 

Hardness 

The hardness of the material grows in importance with the age of con- 
crete. Because of the rounded surface of the aggregate, gravel concrete 
one month old may be weaker than concrete made with comparatively soft 
broken stones; but when one year old, it may surpass in strength the broken- 
stone concrete, because, as the cement becomes harder and the bond firmer, 
the resistance of the aggregate to stress becomes a more important factor. 

The grains should offer at least as high a resistance to crushing as does 
the cement after attaining its maximum strength. In comparing sands of 
the same kind, those having the highest specific gravity are likely, as a rule, 
to be the strongest. This applies in a general way to the comparison of 
different kinds of rock also. 

Value of Different Rocks 

Different rocks of the same class vary so widely in texture and strength 
that it is impossible to give definitely their relative values as aggregate. 
However, a comparison of a large number of tests of concrete made with 
broken stone from different kinds of rock material indicates that its value 

14 



as an aggregate is largely governed by the actual strength of the stone itself, 
the strongest stone producing the strongest concrete. 

Comparative tests discussed by various writers indicate that, in the 
order of their value for concrete, the different materials stand approximately 
as follows : 

1. Granite. 

2. Trap-rock. 

3. Gravel. 

4. Marble. 

5. Limestone. 

6. Slag. 

7. Sandstone. 

The grading, that is, the relative size and quantity of the particles of an 
aggregate, determines in a large measure the density of the mass, which 
greatly affects the quality of the concrete. A coarse, well-graded aggre- 
gate produces a denser and stronger concrete or mortar. A sufficient quan- 
tity of fine grains is valuable in grading the material and reducing the voids, 
but an excess has a tendency to diminish the compression strength con- 
siderably. 

Weights and Voids 

A high unit weight of material and a corresponding low percentage of 
voids are indications of coarseness and good grading of particles. However, 
the impossibility of establishing uniformity of weight and measurement 
due to different percentages of moisture and different methods of handling 
makes these results merely general guides that seldom can be taken as 
positive indications of true relative values. This is especially true of the 
fine aggregates in which percentages of voids increase and weights decrease 
with the addition of moisture up to about 6 per cent. 

Maximum Size 

Within reasonable limits the strength of concrete increases with the size 
of stones. For mass concrete the practical maximum size is 23^ or 3 inches. 
In thin reinforced structures, such as floors and walls, the size must be such 
as can be worked readily about the reinforcing metal, and 1J^ inches is 
generally the maximum. 

Cleanliness 

As stated, the particles of rock should be free from dirt and dust, and 
should not be used when even partly covered with clay; such impurities 
prevent the cement from obtaining a bond on the surface of the particles, 
and often contain materials which retard the hardening of the mortar or 

15 



concrete and prevent it from acquiring normal strength within a reasonable 
length of time. 

An excess of clay or dirt in any form also affects the color of the con- 
crete when hardened, and necessitates more thorough mixing. 

Shape of Particles 

The shape o*f the rock particles influences the strength of the mortar or 
concrete. Flat particles pack loosely and generally are inferior to those of 
cubical fracture. 

Analysis 

The chief value of an analysis of any sand results from the comparison 
of its various properties witK those of other sand tested under similar con- 
ditions and recognized as of a good quality. 

Classification 

The sands in common use as aggregate throughout the United States 
are sedimentary, hence the classification can usually be confined to the 
degree of consolidation and the kind of material, on the basis of whether 
its formation is chiefly siliceous or calcareous. Hardness and texture are 
ready aids in these determinations, which may be conducted in an elemen- 
tary manner. 

The natural sands are usually siliceous, but they vary in degree of con- 
solidation, which determines in a large measure the crushing strength and 
durability of the concrete. Their durability is also dependent upon the 
nature and amount of impurities present, as feldspar, mica, oxides of metals, 
etc. Such impurities account largely for the variegated coloring in sand 
grains. 

Specific Gravity 

As sands or rocks of the same kind and having the highest specific 
gravity are likely to be strongest, a determination of the specific gravity of 
different sands is valuable, since it is a ready indication of the nature and 
hardness of the material. As a rule, sand having the highest specific grav- 
ity, other things being equal, will give the best results. 

The specific gravity of a material is determined by dividing its weight 
by the weight of the water which it displaces when immersed. Take a 
convenient amount of sand, screen it through a J^-inch screen, dry, and 
weigh. Then place some water in a glass graduate, read the height of the 
water, add the sand, and again read the height of the water. The differ- 
ence in readings will be the amount of water displaced by the sand. Divide 
the weight of this water into the weight of the sample of sand. The result 

16 



will be the specific gravity of the sand. (For detailed methods of testing 
sand and cement-sand mortar, Bulletin No. 33, of the United States Bureau 
of Standards, should be referred to.) 

Determinations Necessary 

Physical Analysis. — The determinations necessary for a good physical 
analysis of sand are: 

1. Strength and density in mortar. 

2. Gradation and effective size of grains. 

3. Cleanliness, including per cent, and nature of silt. 

4. Percentage of voids. 

Density 

In the study of sands, a determination of their density is important as 
regards both quality and economy. Other physical conditions being equal, 
the sand which produces the smallest volume of plastic mortar when mixed 
with cement in the required proportions makes the strongest and least per- 
meable mortar, and the densest mortar will be the strongest. This requires 
that the sand be graded from coarse to fine, the coarser particles predominat- 
ing. (The question of determining density will be discussed in the lesson 
on Proportioning, Mixing, and Placing.) 

Gradation and Effective Size 

Sand in which coarse grains predominate will produce a greater strength 
in mortar than that made up of fine grains, because it presents a more com- 
pact mass, as well as a smaller amount of surface area to cover with cement, 
and usually a smaller percentage of voids. A fine sand requires more thor- 
ough mixing than coarse sand in order to get a proper distribution of cement. 

The size of sand grains is so important that it is often profitable to ship 
a coarse sand a considerable distance rather than use a local fine sand. 
Feret, the French authority, computed that it was more economical to use 
coarse instead of fine sand, even though the cost is several times as great. 
It does not follow, however, that because coarse particles have the smallest 
area per unit of volume, the aggregate should all be large. Particles of the 
same size form a volume having a larger percentage of voids than if graded 
in size, hence requiring a larger proportion of cement to produce the maxi- 
mum strength. 

Granulometric Composition 

The determination of the granulometric composition or mechanical 
analysis of sand is made in order to study its properties and to judge of its 
value compared with other sands, and, if necessary, regrade its grains so 
that a denser mass may be secured. 

2 17 



That the strength, quality, and value of a sand may be indicated by 
ascertaining whether the majority of its particles are coarse, medium, or 
fine has been generally established, and it is also important to determine 
the relative degree of coarseness and fineness. 

The percentages of different size grains are frequently determined by a 
mechanical analysis. The sample is first screened through a number of 
sieves of successive sizes, and the percentage by weight retained on each 
recorded. 

For this work the following sieves are recommended : 

COMMEECIAL No. OF SlEVE 

4 

10 

20 

30 

40 

50 

80 
100 
200 

A standard sieve is made of woven brass wire, set into a hard brass 
frame, 8 inches in diameter and 2)4 inches deep. These sieves are described 
by numbers corresponding approximately to the number of meshes per 
linear inch. 

All material referred to as sand must pass a No. 4 sieve. Not more than 
20 per cent, should pass a sieve having 50 meshes per linear inch, and not 
more than 5 per cent, should pass a sieve having 100 meshes per linear inch. 

The tabulated results showing the percentages by weight retained on the 
different sieves form a valuable basis for a study of the effective sizes of 
grains, and for comparison with other sands whose value in mortar or con- 
crete has already been determined. 

Cleanliness 

The effect of dirty sand is dependent upon the quantity and nature of 
the impurities and the form and manner in which they are present. The 
manner in which silt is contained in sand may be determined by inspection. 
The silt in a sand is that material which in solution and in suspension is 
carried away in wash-water so applied as not to remove the small grains of 
sand. This amount may be ascertained by determining either the amount 
of substance contained in the wash-water or the amount of loss sustained by 
the sand through washing. The latter method is more generally used. 

18 



If the silt is vegetable matter in a gelatinous or viscous state, forming a 
colloidal covering over the surface of the sand grains, its presence may be 
determined by immersing the material in a dilute solution of sulphuric or 
hydrochloric acid and comparing the strength of cement mortar made from 
the sand before immersion and after the sand has been treated with the 
dilute acid and thoroughly cleansed by washing. 

Voids 

Voids are air-spaces between the grains and are usually referred to as a 
percentage of the whole. A sand consisting of grains all uniform in size will 
present the maximum of voids. This can be illustrated as follows: Perfect 
spheres of equal size piled in the most compact manner leave, theoretically, 
but 26 per cent, of voids. The only requirement is that the spheres be of 
equal size. Suppose, now, that the spaces between such a pile of equal- 
sized spheres were filled with other perfect spheres of diameter just sufficient 
to touch the larger spheres, the voids in the total included mass would be 
reduced theoretically to 20 per cent. ; and should this be followed up with 
smaller spheres, the air-spaces or voids could be reduced sufficiently to make 
the mass water-tight. Practically, however, a mass of equal-sized spheres 
will be found by experiment to contain about 44 per cent, voids, which may 
be reduced as indicated above. The shape of the particles also affects the 
percentage of voids. Round particles compact more readily and firmly 
and with less difficulty than angular particles. 

Conclusion 

The scope of concrete work has become so great that it demands a 
nation-wide study of aggregates. But such study alone will not solve all 
the problems and insure good work in the future. It will, however, serve to 
give an idea of the relative merits of the various aggregates available. We 
now have standard specifications which demand certain requirements from 
the cement manufacturers. How much more do we need standard speci- 
fications for the selection of concrete aggregates? The preceding para- 
graphs have, in a brief way, given you some idea of the properties required 
in good aggregate, which are, briefly, good grading, cleanliness, and dura- 
bility. Therefore, with good aggregates, standard Portland cement, and 
careful and efficient workmanship, good concrete can easily be obtained. 

REFERENCES 

"Concrete, Plain and Reinforced," by Taylor and Thompson. Published by John 

Wiley and Sons, New York. 
"Materials of Construction," by J. B. Johnson. Published by John Wiley and Sons, 

New York. 
"Engineering Geology," by Ries and Watson. Published by John Wiley and Sons, 

New York. 

19 



HI. Proportioning, Mixing, and Placing of 

Concrete 

I. Proportioning 
Theory 

In order to comprehend the importance of correctly proportioning the 
ingredients used in the making of concrete we must in the beginning obtain 
a correct idea of the theory of the material we propose to manufacture. 

The aggregates consisting of sand and gravel or broken stone are wholly 
inert until combined with Portland cement. Consequently it is of prime 
importance that every piece of coarse aggregate be thoroughly surrounded 
with sand-cement mortar and that every grain of sand be inclosed in a film 
of neat cement. In so far as actual practice departs from this fundamental 
principle, just so far will the bonding be defective. 

The second important principle of concrete composition is that voids 
shall be eliminated by such gradation of materials that the spaces between 
larger pieces of the coarse aggregate will be occupied by smaller pieces, and 
the spaces between these will in turn be filled by sand until in a perfectly 
proportioned mixture there will remain only such voids as will be taken up 
by the cement paste when the concrete is finally compacted in the place of 
its ultimate use. The absolute elimination of voids is an ideal condition, 
hence it is essential to use every means in our power toward approaching 
the perfection suggested. The more nearly we approximate the theoretical 
possibility, the more successful we shall be in actual practice. 

Object 

Both strength and density in finished concrete construction are depend- 
ent upon careful proportioning. A very porous concrete may, under certain 
conditions of manufacture, be stronger than a seemingly dense concrete 
which is lacking in cement or in coarse aggregate. Hence we observe work 
disintegrate after two or three years, and upon examining a fracture find 
that the concrete has no large voids, but is composed of fine sand with little 
or no coarse aggregate. Such material may appear dense, but hardly de- 
serves to be called concrete. 

On the other hand, remarkable instances of strength developed in porous 

20 



concrete may be observed where the coarse aggregate was fairly well graded 
and but little sand used. This practice is not recommended because the 
working conditions might not be identical, and a concrete possessing a large 
percentage of voids will not be water-tight. The point is mentioned merely 
to emphasize the fact that coarse aggregate and cement give strength to 
concrete. Sand increases the density. 

Impermeability, or resistance to the passage of water, is one of the most 
prominent characteristics of good concrete and is absolutely dependent 
upon the elimination of voids, which results only from correct proportioning 
of ingredients. A porous concrete is never water-tight. Quite a number of 
processes for waterproofing have been suggested; some, like soap and alum, 
or the " Sylvester Process," are public property, while others are either 
secret formulas or process patents. Some consist of incorporating com- 
pounds in the concrete at the time of mixing, and others of applying com- 
pounds to the exterior or interior of the work after completion. If the con- 
crete is properly proportioned, there is no reason for using any integral 
waterproofing medium. 

In reinforced concrete work a satisfactory bond between the steel and 
concrete can be obtained only by such careful proportioning as will insure 
a concrete practically free from voids. This does not mean merely slushing 
in water enough to fill spaces between aggregate surrounding rods or other 
reinforcement. Surplus water will disappear by evaporation, leaving cavi- 
ties adjacent to the reinforcement, and when a failure occurs, rods will be 
found pulled out of porous concrete, the porous concrete not offering suffi- 
cient bond to transfer the stress to the steel reinforcement. 

Methods of Proportioning 

One method of proportioning is by measuring the amount of water 
required to fill the voids in the coarse aggregate, and using a like proportion 
of sand, in turn measuring similarly the voids in the sand to determine the 
required proportion of cement. This method of proportioning is inaccurate 
and cannot be recommended for general use. 

Another method consists of ascertaining the specific gravity of the 
material to be used, then weighing a fixed volume of the sand, gravel, or 
broken stone in the condition in which it is to be used, and from the differ- 
ence between the weight of like volumes of solid and loose material determin- 
ing the percentage of voids. This method is scientifically correct, but will 
seldom be used outside of laboratory practice on account of the equipment 
required to make the computation accurately. 

There is no doubt that density proportioning is the most practical and 
definite method yet evolved. While it is largely a cut and try method, 
and should be checked by cylinder compression tests, there are fewer possi- 

21 



bilities of error and the results are not dependent on the use of delicate 
apparatus. The density test has its value in the determination of the 
proper amount of coarse aggregate to use with a given mortar. This does 
not mean, of course, that the determination of mortar density is not of great 
value in obtaining the relative merits of two given sands, as it might 
develop in an analysis of this kind that one sand would work better than 
another in lean mixtures and poorer in rich mixtures. Take a fixed weight 
of dry coarse aggregate and one-half the same weight of dry sand. Shake 
them down in a cylindrical vessel and mark how high the mixture fills the 
vessel; then try another mixture of the same total weight, but using less 
sand and more coarse aggregate, or a mixture of like weight using more sand 
and less coarse aggregate. The relative proportions by weight which will 
occupy the least volume are the proportions containing the smallest possible 
percentage of voids. This method is very effective and requires neither 
apparatus nor technical skill. If conditions require proportions by volume 
rather than weight, as is generally the case, the experimental process will be 
reversed, measuring the materials placed in the cylinder and trying different 
compounds to ascertain which gives the greatest weight for the same total 
volume. 

In proportioning by volume a sack of cement will be considered as one 
cubic foot ; in proportioning by weight, a sack of cement may be accepted as 
94 pounds net. In determining the amount of cement necessary to fill 
voids in sand, several experimental mixtures should be prepared in different 
proportions and the tests conducted as already described for the inert 
materials. This method of determining the composition of mortars is also 
highly recommended for determining a choice between two or more sands 
of like composition, because the sand which gives a mortar of least volume 
for like weights will always make the densest concrete. 

Sizing Materials 

Unless sand and gravel are purchased separately, it will be necessary to 
separate them by screening to arbitrary sizes before proportioning. If, for 
instance, it is proposed to use bank gravel varying in size from fine sand up 
to small boulders, two screens should be used, the first rejecting everything 
exceeding the maximum size of aggregate suitable for the work, this varying 
from z /i inch for fence posts and block up to 2 inches for foundations and 
other work of large cross-section. The general rule for wall is that the 
largest size of aggregate shall not exceed, in its greatest diameter, one-half 
the thickness of the wall. The second screen should in all cases be of }/&- 
inch mesh, the particles retained upon it to be regarded as coarse aggregate, 
and those passing it as fine aggregate or sand. 

22 



Average Proportions 

As many users of concrete do not wish to take the trouble to test their 
own materials, it is customary for them to use the proportions which have 
been found to produce satisfactory results under average conditions. 
These are one part of cement, two and one-half parts of sand, and four parts 
of coarse aggregate (expressed 1:2:4) for most classes of construction. 
In the manufacture of products large enough to use aggregate exceeding one 
inch in greatest dimension the proportion of coarse aggregate may be in- 
creased accordingly. Conversely, where a fine texture is desired for orna- 
mental purposes, the proportion of cement must be increased, reaching its 
maximum in 1 : V/2 troweled surfaces. The following table gives the pro- 
portions recommended for various classes of work : 

A 1:2:3 mixture for: 

One-course concrete highway, street, and barnyard pavements. 

One-course floors and walks. 

Roofs. 

Fence-posts and for sills and lintels without mortar surface. 

Water-troughs and tanks. 

A 1:2:4 mixture for: 

Reinforced concrete floors, beams, and columns. 
Large engine foundations. 
Work subject to vibration. 
Building walls above foundation. 
Silo walls. 

1 : 23^2 • 4 mixture for : 

Base of two-course street and highway pavements. 
Backing of concrete block and similar cement products. 

A 1:3:5 mixture for : 

Supporting walls and foundations. 
Small engine foundations. 
Base of sidewalks and two-course floors. 
Mass concrete footings, etc. 

Mortar 

1:13^2 mixture for: 
Wearing course of two-course floors. 

1:2 mixture for: 
Scratch coat of exterior plaster. 
Facing blocks and similar cement products. 
Wearing course of two-course walks, street, and highway pavements. 

1 : 2Y2 mixture for : 
Finish coat of exterior plaster. 
Fence-posts when coarse aggregate is not used. 

23 



1:3 mixture for: 

Concrete blocks when coarse aggregate is not used. 
Cement drain tile when coarse aggregate is not used. 

Amount of Water 

The consistence will depend upon the use for which the concrete is in- 
tended and upon the process of manufacture necessarily associated there- 
with. 

Three consistencies or mixtures, determined by the amount of water 
used, are generally called the dry, the quaky, and the wet. The dry mix- 
ture is of the consistence of damp earth, and is used where the concrete 
is tamped into place, being principally useful in steel molds for making 
products requiring no reinforcement, such as brick, block, and ornamental 
cases. 

The quaky mixture is- so named because it is wet enough to quake or 
shake when tamped. It is used in all molded products requiring reinforce- 
ment, such as fence-posts, lamp-posts, telegraph and telephone poles, drain 
tile, sewer-pipe, ash-pit rings, and the like; also in engine foundations and 
the footings of buildings. 

The wet mixture contains sufficient water to permit of its flowing from 
a shovel or wheelbarrow, but not enough to cause a separation of the par- 
ticles. It is used in building reinforced concrete structures, such as silos, 
barns, dwellings, and other buildings where the concrete is allowed to 
remain undisturbed in the forms for several weeks. The scum (or laitance) 
should be scraped from the surface of green concrete and the surface thor- 
oughly scrubbed and moistened before placing additional concrete. 

There is a pronounced tendency at the present time to use too much 
water. This results in concrete which is porous and of very low initial 
strength. There are very few instances in actual construction work where 
a plastic wet mix will not be satisfactory and a word of warning should be 
sounded against the use of very wet, sloppy mixtures. 

II. Mixing 

Fundamental Principle 

The importance of thoroughly and carefully mixing the ingredients used 
in the manufacture of concrete is secondary only to .the proportioning, 
because the mixing cannot be done until after the proportioning has been 
accomplished. It is secondary in time, but equal in importance. 

As stated earlier in this lesson, an essential feature of concrete construc- 
tion is the coating of every grain of sand with a film of neat cement, and the 
coating of every piece of coarse aggregate with sand-cement mortar. This 
statement may be emphasized by stating that it is the fundamental prin- 

24 



ciple of all concrete construction; an earnest effort to accomplish this result 
will insure success. 

In machine mixing experiments show that for periods up to two minutes 
the strength of concrete made from the same materials and with the same 
percentage of water is proportional to the time it is kept in the revolving 
mixer. 

Assuming that proper proportions have been determined, the result so 
carefully sought can be attained only by thorough and intelligent mixing. 

Shovel Mixing 

Let us first consider the rather difficult problem of securing satisfactory 
results where the volume of work does not warrant the installation of a 
mixing machine. 

The first requirement will be a water-tight platform large enough for two 
men to shovel conveniently from either end as large a batch of concrete as 
can be used within thirty minutes after water has been added to it. 

If, on account of meal-time or any emergency, a portion of a batch lies 
until the cement has become partially hardened, throw it away rather 
than jeopardize the work. 

As proportioning is usually done by volume, one cubic foot is a conve- 
nient unit, as it allows full sacks of cement to be used. The required amount 
of sand should first be spread upon the mixing platform, after which the 
cement should be spread in a layer on the sand. Two men, using square 
pointed shovels, will then turn the sand and cement over two or more times 
until the streaks of brown and gray have merged into a uniform color 
throughout the mass. The coarse aggregate is then added and the mix- 
ing continued, water being added during the first turning after adding 
coarse aggregate. Water should be added gently, as from a hose nozle or 
the spout of a watering-pot, in order to prevent washing out the cement. 
Turning should continue until the mortar is of uniform consistence through- 
out, which will usually require at least three turnings after adding water. 

Mixing in the above manner will give satisfactory results, but the labor 
involved is considerable, and on this account it is too common for those 
attempting it to slight the work and use the concrete in an imperfectly 
mixed condition. 

Machine Mixing 

Mixers have been brought to a high state of efficiency, and to-day there 
are many on the market designed to produce the best results at minimum 
cost of labor and power. While it is beyond the scope of this lesson to dis- 
cuss mixers, we may, in passing, mention one or two of the principles which 
will assist the concrete manufacturer in making a selection suited to his 

25 



needs. The batch-mixers, whether cubes, cylinders, or truncated cones, 
allow the material to be introduced in any order desired, provided only that 
each separate batch contains the proper relative proportions of ingredients. 
After the batch has been placed in the mixer, it is revolved for a specified 
time, or a definite number of revolutions, until either by the shape of the 
drum itself or by means of deflectors therein the cement, sand, and coarse 
aggregate have been thoroughly mixed. Most batch-mixers are equipped 
with a small tank from which a pipe leads into the mixer, and when the 
materials have been sufficiently mixed in a dry state, water is sprayed on 
them while the revolutions of the mixer continue. 

The continuous mixer consists mainly of a number of hoppers for the 
several materials, placed over one end of a semi-circular trough containing 
blades or shovels fixed to a rotating shaft. The motive power is generally 
supplied by a gasolene engine or an electric motor. The dry materials are 
fed automatically from the hoppers into the trough, mixed, and carried 
along by the blades to the discharge end, water being added; meanwhile 
the concrete is discharged continuously. 

The batch type of mixer is considered by the majority of engineers to 
give the best results because the measuring of the materials can be posi- 
tively regulated, whereas with the continuous mixer variations in the amount 
of moisture in the sand or fluffiness of the cement will cause a variation in 
the relative proportions of these materials in the mixture. On this account 
engineers favor the batch-mixer. 

Lists of manufacturers of mixers will be found in the columns of current 
concrete periodicals. 

III. Placing 

Final Problem 

But when all is said and done : when we have selected the best materials, 
have ascertained the proper proportions of each and the correct amount of 
water for the consistence required to serve our particular purpose; when by 
shovel or machine we have combined the different materials required to 
make concrete, we have produced a mass of material which must be care- 
fully deposited, compacted, and made to take some one of the thousand 
and one shapes which concrete assumes. 

This, then, is our problem, the placing of the concrete, and we shall find 
three distinct methods of accomplishing this result: 

Pressure and Tamping 

Whenever a dry mixture is used in steel molds to produce such unrein- 
forced products as ornamental vases, block or brick, concrete is placed by 

26 



pressing or tamping. If pressure is applied, it will ordinarily be by means 
of a press simplifying the process and making it necessary only to see that 
the molds are adequately and evenly filled in order that the product may be 
uniform in density. If, however, tamping is the method employed, con- 
siderable supervision will be found necessary, as the quality of the product 
may vary considerably unless the tamping is uniformly performed. It is 
particularly necessary that the mold be tamped while filling, not filled and 
tamped afterward. The latter method will not only fail to fill the lower 
corners, but will make one-half of the molded product much denser than the 
other. If tamping is well done by one man (or two, if a large mold) while 
the mold is being filled by another, there is no reason why the product 
should not be perfectly satisfactory and as uniform as though made under 
mechanical or hydraulic pressure. To secure more uniform density and 
effect a saving of labor, power tampers are used, the multiple tampers being 
especially serviceable in making block and brick. 

Agitation 

Neither tamping nor pressure will be of service in the case of those 
products requiring the introduction of reinforcement, such as tile, pipe, 
poles, and posts. In the manufacture of these and similar products the 
steel, in whatever form required for reinforcing, is introduced at the proper 
place in the mold while it is being filled, with a quaky mixture of concrete 
which is compacted, forced into corners and around or through the reinforce- 
ment, by vigorously stirring the mixture and jarring the mold. 

Depositing Wet Concrete 

Placing concrete for reinforced concrete structures, including silos and 
all sorts of buildings, involves work on a scale warranting the installation of 
special apparatus to save both time and labor in transporting the concrete 
from the mixer to the place of use. Elevators, dump-cars, and chutes are 
ordinarily used in the construction of reinforced concrete buildings. In 
constructing silos it is economical to provide a center hoisting device with 
derrick and an automatic dumping bucket. 

The concrete is poured into forms in which reinforcement has previously 
been placed. It is then necessary to spade it back from the forms in order 
to prevent large pieces of aggregate from retaining surface positions when 
the forms are removed. The larger pieces of aggregate should, as far as 
possible, be forced away both from the reinforcement and the forms, so that 
they may occupy an intermediate position. Though the subject of forms is 
treated in another lesson, a word of caution relative to their removal may 
not be amiss at this time. While no definite rule can be given to fit all local 
conditions and variations of structure, humidity, and temperature, good 

27 



judgment will suggest that too early removal involves danger, while reason- 
able delay in removing forms is a wise precaution, insuring safety. 

REFERENCES 

" Concrete, Plain and Reinforced," by Taylor and Thompson. Published by John Wiley 

and Sons, New York City. 
" Concrete Costs," by Taylor and Thompson. Published by John Wiley and Sons, 

New York City. 
" Reinforced Concrete Construction," by Buell and Hill. Published by McGraw-Hill 

Book Co., New York City. 



IV. Forms 

Introductory 

The plasticity of concrete, and the readiness with which the material can 
be adapted to all shapes and sizes of construction, have from the beginning 
of the more extensive use of concrete made the production of molds of 
desired form a very important consideration in all concrete construction 
work. While iron and steel molds have been used for small members, such 
as block and brick and ornamental pieces, in which the same design and 
size can be indefinitely repeated, larger concrete construction requires indi- 
vidual design, determined by local conditions and particular needs. The 
ease with which concrete may be adapted to such peculiar requirements of 
individual use is one of the chief merits of the material. Consequently, 
means must be provided for constructing, at or near the place where the 
concrete is to be used and from materials easily procured, molds which may 
be made to fit the circumstances of each individual case. Molds of this 
diversified character are commonly called forms. 

Classification 

Forms may be roughly classified as follows: 

1. Rectangular forms wholly of lumber. 

2. Rectangular forms using metal fastening devices! 

3. Rectangular metal forms. 

4. Circular forms of wood and sheet metal. 

5. Circular forms wholly metal. 

6. Miscellaneous. 

Lumber Forms 

Contrary to the usual practice in building construction, green lumber 
will keep its shape in all rectangular forms better than lumber that is thor- 
oughly dry. If dry lumber is used, it should be thoroughly wet before the 
concrete is placed. The use of oil or grease free from animal oils or fats on 

28 



the inside of forms is recommended, as it prevents absorption of water from 
the concrete by the forms and makes their removal easier. Where any fine 
ornamentation is used, the molding or other device introduced to vary the 
surface should be painted with equal parts of boiled linseed oil and kerosene, 
it is, however, essential that forms should be thoroughly cleaned each time 
they are used, and that no dry concrete be left sticking to the face of the 
forms. Forms may be built from stock length lumber, requiring very little 
sawing and permitting of the lumber being used later for other purposes. 
White pine is considered the best lumber for forms, although spruce, fir, and 
Norway pine are often used. The face of forms should be free from loose 
knots, slivers, or other irregularities, as concrete will reproduce them all with 
great faithfulness. Matched lumber may be used to afford a smooth finish, 
and very satisfactory results can be obtained by proper care in the con- 
struction of forms. 

Rectangular Forms 

In the construction of rectangular forms the first type of construction 
presenting itself for consideration is foundation work. Where the excava- 
tion is made simply for a foundation without cellar or basement, the soil will 
often be firm enough so that the trench, if carefully excavated, may be used 
as a form below ground fine. In this case the edges must be protected to 
keep the dirt out of the concrete. In carrying the foundation from the 
ground line to the level of the first floor, forms must be constructed resting 
upon a bridge and extending slightly below the ground line. These forms 
may be constructed in sections or built in place. 

If the inner and outer parts of the form are built separately, they must, 
when put into position, be leveled and plumbed carefully. Whether built in 
sections or built in place, forms must be braced thoroughly and tied to- 
gether, as the essential duty of any form is rigidly to maintain its integrity 
until the concrete has hardened. 

Forms for foundation piers and for the foundation of all kinds of ma- 
chinery are constructed in substantially the same manner as for regular 
building foundations. The construction of machinery foundations is essen- 
tially a problem of securing the necessary mass and weight, consequently 
the greater part of the foundation will be under ground, and all that is 
required above ground is an open box of sufficient strength to maintain the 
concrete in the desired form while hardening. 

Where the excavation for cellar is made by team and scraper, the sides 
will not be perpendicular, and the excavation will usually be somewhat 
larger than the dimensions of the cellar-wall. Consequently it is necessary 
to use both inner and outer forms. Each form is braced by uprights spaced 
close enough to prevent any spreading or bulging of the sheeting when sub- 

29 



jected to the outward pressure of the fresh concrete. The inner form should 
be securely braced in. a perpendicular position by lumber braces from the 
floor of the excavation. The outer form should be fastened to the inner 
form by wires running through both near the bottom, and at the same place 
the forms should be separated by spacing blocks of the width determined 
upon for the cellar wall. The outer form should, like the inner, be perpen- 
dicular unless a slight batter is desired, in which case the spacing blocks 
should be lengthened to spread the bottom of the forms apart and increase 
the thickness of the wall at the bottom without interfering with the estab- 
lished thickness of the wall at the top. The wires connecting the two forms 
should be drawn tight by twisting with a large nail or rod until the forms are 
drawn firmly against the spacing blocks. The top of the uprights should be 
joined by cleats. The method just described produces a very rigid form. 

When an outside cellar or basement entrance is desired, the forms for 
same should be constructed simultaneously with the cellar wall forms. 
When in position, these forms will rest upon the floor of the excavation made 
for the steps. If the excavation for the entrance is carefully made, only the 
inside form will be required until ground line is reached. As the walls will 
project above the ground where they join the building and slope from that 
point to the opposite end of the entrance, an outside form will be required 
above the ground line. By properly bracing the form, one side wall may be 
made, and after it has hardened the form reversed and used for the other 
side. After both side walls have been made, forms for the steps giving 
desired height of riser and width of tread may then be securely braced 
between the side walls. 

In the construction of double walls, such as in ice-houses, the intervening 
air-space is not usually wide enough to accommodate two sets of forms. 
Therefore the hollow wall is usually constructed by placing in the forms 
cores which are later withdrawn. 

Forms for walks and floors should consist of 2-inch lumber, in width 
equal to the desired thickness of the walk or floor, staked in the earth to 
form slabs of the desired size. The concrete is mixed wetter than for two- 
course work, and where the walk or floor is laid in one course, slabs should 
be laid alternately, allowing cross forms to remain in place until ready to fill 
intermediate slabs. This method is also used extensively in two-course 
work, although many prefer to work consecutively, moving the cross-piece 
each time a slab is completed. If laid continuously, care must be exercised 
to preserve the vertical joints through the entire walk. Horse blocks or 
carriage steps may be constructed where the walk joins the driveway by the 
use of simple box forms. 

The modern farmer is making use of concrete for the construction of 
various types of tanks, such as the stock watering tank, the hog feeding 

30 



trough, the dipping vat, and the hog wallow, all of which may be constructed 
by the use of rectangular lumber forms. 

The general method of constructing rectangular tanks above ground 
consists in erecting an outer form, usually of 2-inch lumber, in which the 
concrete floor of the tank is placed, and the surface finished as desired, after 
which the bottomless inner form, which must be previously prepared and 
read}' for immediate use before the previously placed concrete has hardened, 
is quickly inserted and securely fastened in place by cleats joining the up- 
rights of the outer and inner forms. The method of constructing rectangu- 
lar tanks underground differs only in that the earth usually forms the outer 
form and a wood form is required for the roof. In constructing septic tanks 
provision must be made for the several partitions and compartments neces- 
sary to secure decomposition of the sewage and disposal of the effluent. 

Two methods are used with equal satisfaction in manufacturing small 
troughs, which need not necessarily be built in place. One is to use a box 
mold and finish the interior with a straight batter or a concave surface by 
striking it out with a templet. The other method is to use a core of firm 
clay or wood made in shape to correspond with the inside of the trough. 
A bottomless box is placed over the inverted core, and by filling the box 
with concrete and striking it off level, the trough is manufactured upside 
down. 

The simplest deviation from home-made molds is to purchase clamps for 
holding forms in place, thus doing away with nailing them to the uprights. 
There are several systems of clamps on the market, some of which are very 
ingenious, and all of which are designed with two purposes in view, the first 
being to facilitate the erection and removal of forms, and the second being 
to save loss of lumber from repeated nailing and tearing down. 

A still wider departure from the home-made forms brings us to those 
constructed wholly of metal, which provide a rapid and economical method 
of concrete construction where a large amount of work is to be done along 
uniform lines. Only continued repetition, however, will justify the pur- 
chase of metal forms. Where the opportunity occurs to rent metal forms 
for any work of considerable importance, a saving may be effected and the 
quality of the work somewhat improved on account of greater surface 
uniformity secured by use of the metal forms. 

Circular Forms 

Circular forms are extensively used in the construction of tanks because 
a round tank is more economical to build and will -resist frost action better 
than a tank of any other shape. The construction of a circular form pre- 
sents greater difficulty than does that of a rectangular form, and it is usually 
better for several of those who desire to construct tanks to determine upon 

31 



a standard size and join in the use of a set of forms, or, if this cannot be 
done, a set of forms may be rented if but a single tank is to be made. For a 
10-foot circular tank, 2 feet 6 inches in depth, the forms usually cost about 
$50, while the cost of the tank itself, exclusive of sand and gravel, is only 
$30. Forms for circular tanks consist of an inner and an outer wooden 
frame covered with sheet iron. Silo forms may be used for the outer forms 
of large tanks. The height of the inner form is equal to the inside depth of 
the tank, and the height of the outer form is equal to the sum of the inside 
depth and the floor thickness of the tank. After the inner and outer circles 
of the form have been laid out, segments are cut from 1-inch lumber and a 
wooden frame is built up, fence fashion. No. 22 gage galvanized iron is 
then attached by screws or nails. The inner form should slope toward 
the outer one, to give proper batter to the inside of the tank, and prevent 
bursting in case of freezing. 

The selection of silo forms presents to the modern farmer one of the 
most important problems in connection with the use of concrete. What are 
known as home-made silo forms are usually constructed in 3-foot sections, 
but it is hardly desirable to construct a set of forms for the express purpose 
of building one silo. It is far better for farmers to unite in the matter, as a 
set of forms may be used for constructing a large number of silos. How- 
ever, if one must build his own forms, a most ingenious model is that of Mr. 
David Imrie, Roberts, Wisconsin, who has introduced his form to hundreds 
of farmers in connection with the work of the Wisconsin Farmers' Institute. 
The inner form consists essentially of hooped sheet metal securely clamped 
and braced. No. 28 gage galvanized sheet iron is used, and the form is 
assembled in eight segments which are bolted together. The outer form is 
made of 18 or 20 gage galvanized sheet metal 3 feet in width, in two or more 
pieces, joined by heavy band iron riveted to the ends of each piece, which is 
turned at right angles and drilled to receive the bolts drawing adjoining 
sections together. Forms of this type have been built at a cost varying 
from $25 to $50. 

Practically all silos now built are roofed. The construction of the roof 
form is a simple matter, requiring only a box for the cornice and 2 inch by 
6 inch rafters radiating from the apex to the roof edge, on which 1 inch by 
6 inch sheeting is laid to receive the concrete. 

Many commercial systems of silo construction are now upon the market. 
Fortunately, most of them are meritorious and will result in more satis- 
factory work than can be obtained from home-made molds inasmuch as 
they effect many economies in the methods of handling materials and 
assembling the forms. The various commercial silo systems are operated 
under different methods. The forms are constructed wholly of metal, and 
some companies sell them outright to an association of farmers who desire 

32 



to construct silos; some companies rent their forms for the construction of 
a single silo; some companies construct a silo for the farmer, acting in the 
capacity of contractors and guaranteeing their work in every way. 

Miscellaneous Forms 

The miscellaneous uses of concrete about the barn, barnyard, and farm 
in general are innumerable. The preparation of forms for the many uses to 
which concrete may be put affords pleasant exercise for the ingenuity of any 
one familiar with the uses of concrete. A few of the possibilities of smaller 
construction are merely suggested: concrete stalls, mangers, hens' nests, 
hotbeds, pits for wagon scales, curbing for old wells, pump pits, and waste- 
water receptacles. The form for the last mentioned consists of earth exca- 
vation for the outer form and an empty half barrel for the inner form, which 
indicates how simple concrete construction may be made. 

The removal of the form is a matter requiring very careful consideration. 
A great deal of work has been injured and not a little has failed because of 
undue haste in removing forms. Two or three days' additional time al- 
lowed to new concrete before removing the forms often marks the differ- 
ence between defective and thoroughly satisfactory work. 

REFERENCES 

"Reinforced Concrete Construction," by George A. Hool. Published by McGraw- 
Hill Book Company, New York City. 

"Concrete Costs," by Taylor and Thompson. Published by John Wiley and Sons, 
New York City. 

"Reinforced Concrete Construction," by Buell and Hill. Published by McGraw-Hill 
Book Co., New York City. 



V. Concrete Foundations and Walls 
I. Foundations 

Advantages 

Concrete is especially adapted for use in building foundations because of 
the following characteristic qualities : 

1. Compressive strength. 

2. Durability. 

3. Moderate cost. 

4. Ease of construction. 

5. Adaptability to irregular excavations. * 

6. Capacity for reinforcement. 

7. Can be placed under water. 

Plain, or unreinforced, concrete shows its greatest strength under direct 
3 33 



compression. Carrying capacity is the quality chiefly sought in the se- 
lection of material for the foundation of any building. Moreover, concrete 
lasts forever without repairs, and permanence is a consideration scarcely 
secondary to strength in determining a choice of foundation material. The 
cost of a well-built concrete foundation is considerably less than that of one 
constructed of any other building material of equal strength and durability. 
Under average conditions the time required for building a concrete founda- 
tion is shorter than that required for one of brick or stone. Concrete is the 
only foundation material which readily adapts itself to slopes, change of 
grade, or other irregularities in the subgrade on which the foundation is laid. 
Wherever conditions require a foundation of restricted area on a side hill, 
exposing a portion of the foundation wall to danger of accidental injury, or 
vibration of engines and other machinery must be withstood — in any of 
these cases concrete demonstrates its adaptability by permitting the intro- 
duction of sufficient reinforcement satisfactorily to perform the duty de- 
manded. 

Owing to the fact that Portland cement has the property of hardening 
under water it is now almost universally used for construction work carried 
on below water. Care should always be exercised not to deposit it in 
running water, inasmuch as the water will carry away a portion of the 
cement and thus decrease the strength of the concrete. 

Consequently, concrete is supplanting all other materials for building 
foundations of every character, irrespective of the character of the super- 
structure. Some of the principles which must be observed to secure the 
best results will be here outlined : 

Materials 

The proportioning, mixing, and placing of concrete has been thoroughly 
discussed in another lesson, and the practices therein recommended should 
be rigidly observed. Further, it is often possible in foundation work to 
increase the size of the largest aggregate up to 2 inches or even 23^ inches. 
Wherever large sizes of clean, hard, durable gravel or broken stone can be 
used, additional strength is secured; for this purpose field stones may be 
employed advantageously. 

Excavation 

In preparing for the erection of any rectangular structure a base line 
should first be determined upon, and from the base line the several corners 
should be ascertained by accurate measurement at right angles or at such 
other angles as may be desired in structures of irregular shape. The corners 
should be staked and definitely fixed by a tack driven in the top of each 
stake. All measurements and angles should then be checked back to the 

34 



base line. Several feet outside of the line of stakes other stakes should be 
set to overreach the corners, or a frame maybe built 10 inches above ground, 
called a batten board, from which lines are then run to pass exactly over the 
tacks set in the stakes. These lines show the outside of the proposed exca- 
vation, and by measuring the width of the foundation and running parallel 
lines that far inside of the first lines, the lay-out is ready for excavation. 

The depth and width of excavation depend upon the height and char- 
acter of the building to be erected, but should always go to solid earth, and 
should at least be lower than frost line. If the ground is filled with surface 
water at certain seasons of the year, drainage should be provided from the 
bottom of the foundation trench to a natural outlet. 

Footings 

As. a convenience in setting forms, footings are sometimes provided 
where ground is firm. Wherever a foundation is to be constructed on filled 
ground, which cannot, by rolling and tamping, be made solid enough to 
guarantee the permanent carrying without settlement of the superimposed 
load, the weight must be distributed by a layer of concrete wider than the 
foundation itself. This is known as a footing. It may be twice as wide as 
the foundation, but must be thick enough to prevent shearing or cracking, 
and may have either sloping or stepped sides. In extreme cases of very 
soft earth requiring excessively wide footings cross-bars or reinforcing rods 
are introduced in the footings to distribute the foundation load without 
injury to the concrete slab. 

Kidder ("Architects' and Builders' Pocket-book") gives bearing power 
of soils as follows: 

Bearing Power in Tons 
per Square Foot 

Min. Max. 

Rock — the hardest— in thick layers in native bed 200 

Rock equal to best ashlar masonry - 25 30 

Rock equal to best brick masonry 15 20 

Rock equal to poor brick masonry 5 10 

Clay on thick beds, always dry 4 6 

Clay on thick beds, moderately dry 2 4 

Clay, soft 1 2 

Gravel and coarse sand, well cemented 8 10 

Sand, compact and well cemented 4 6 

Sand, clean, dry 2 4 

Quicksand, alluvial soils, etc 0.5 1 

Concrete for footings should be mixed in the proportions of 1 sack of 
Portland cement, 3 cubic feet of clean, coarse sand, and 5 cubic feet of 
gravel or broken stone, varying in size from \i inch up to 2 inches; if rein- 
forced, the proportions should be 1:2:4. Enough water should be used to 
form a quaky mixture, but not enough to cause the cement and aggregate 
to separate in placing. Concrete foundations and footings may be keyed 

35 



by partially embedding in the footing vertical rods or horizontal I-beams; 
in light structures a similar effect may be produced by casting on the foot- 
ing a central longitudinal projection which will form a tongue-and-groove 
joint with the foundation. If the placing of the foundation is delayed 
until the footing has hardened, the latter should be cleaned, roughened, 
and wetted, and then grouted with a mixture in the proportion of 1 sack 
of Portland cement to 1 cubic foot of sand, mixed to the consistence of 
thick cream. 

Simple Foundations 

Where there is to be no cellar or basement under a building and the 
nature of the ground is such that the excavation can be made for the exact 
width of the foundation, forms below ground line are unnecessary provided 
the earth is firm enough to prevent " caving in" of the sides. It is, how- 
ever, necessary to protect the edges and sides, especially on the side opposite 
that from which the concrete is poured, by burlap aprons made by tacking 
a piece of burlap on a piece of lumber 2 by 4 inches, long enough to rest on 
cross-pieces bridging the excavation. When the ground line is almost 
reached, forms previously constructed of 1-inch boards on 2-inch by 4- 
inch studding must be placed to receive the concrete from ground line to 
the top of the foundation wall. The forms must not rest on the concrete 
already placed, but upon a bridge which will allow them to drop slightly 
below the ground line. No appreciable time should elapse between plac- 
ing the concrete below and above ground, as an interval of more than thirty 
minutes will produce a line of cleavage, seriously weakening the wall and 
lessening its water-tightness. 

Piers and Engine Foundations 

Foundation piers for additional supports under large or heavily loaded 
buildings are constructed in the same manner as simple foundations, the 
size being determined by the estimated load and the character of the 
ground. The footing is important, as the sole object of such construction 
is distribution of the load. 

Foundations for gasolene or steam engines and for any machinery sub- 
ject to considerable vibration are constructed in the same manner as 
foundation piers. The size and depth are determined by the amount of 
vibration to be withstood. The problem is simply to build in the earth 
a solid block of concrete of weight sufficient to withstand the action of the 
engine bolted to its top. Casings for the bolts are made of 2-inch pipe, 
resting on plates at the lower end of the bolts; they are embedded in the 
concrete and provide for any necessary adjustment of the bolts when 
setting the engine in place. The length of each casing equals the length 

36 



of the bolt to be embedded ; by tightening the nut on each bolt above the 
templet the casing fits snugly against the templet, and the top of the 
bolt is brought to proper height. The templet can be made from 1-inch 
material, and will be sufficient for placing the casings in smaller engine 
foundations; for larger foundations cross-bracing should be added. In 
setting bolts first nail the templet securely in place, then mark accurately 
the position of the bolts, and bore holes only slightly larger than the bolts. 
Be sure the bolt holes are correctly located. Bolts and casings are now set 
in place, centering casings with bolts by several nails or by wooden strips 
lightly nailed on the under side of the templets. Proportions of 1:3:5 
may be used in foundations for gasolene engines and cream separators. 
A mixture of 1:2:4, using aggregate up to 2 inches or 2 Yi inches, is recom- 
mended for steam engines and large machinery. 



II. Walls 

Cellar and Basement Walls 

Wherever the excavation is made for a cellar under a building, the 
problem includes not only the construction of a wall to serve the purpose 
of a foundation for the superstructure, but of one which will also insure a 
cellar warm in winter, cool in summer, and dry at all seasons. Concrete 
walls of suitable thickness solve the problem of heat transmission, and if 
properly built, the cellar will be always dry. Proper drainage should, 
however, be provided. While a concrete cellar wall may be constructed 
so impermeable that water standing outside will not penetrate to the 
interior, drainage to natural outlets is a wise precaution and should not be 
omitted except in soil that is dry all the year around. 

When the cellar excavation (often made by team and scraper) has ir- 
regular sides and is somewhat larger than the actual dimensions of the 
wall, it will be necessary to use both outside and inside wall forms. Only 
in small excavations shoveled by hand and left with true sides in firm earth 
free from indications of caving can the earth be used for the outer form. 

In using forms for both the outside and the inside of the wall quite a 
large amount of lumber would be required if forms for the entire work 
were constructed at one time. To obviate this, forms can be built in sec- 
tions, each section being of the full height of the cellar wall, and as long as 
convenient to build and set in place. An entire section should be filled 
at one operation in order to avoid horizontal joints* or lines of cleavage in 
the concrete. 

At the end of the section a piece of 2-inch by 4-inch lumber, with both 
edges beveled to permit of easy removal, is fastened to the face of the parti- 

37 



tion board used as a stop-off at the section's end. This makes a tongue- 
and-groove vertical joint. When the forms are ready to fill for the adjoin- 
ing section, the end of the partially hardened section must be cleaned, 
wetted, and coated with neat cement grout mixed to the consistence of 
thick cream. Attention is called to the preference in building practice for 
vertical joints in foundation and cellar walls, whereas horizontal joints are 
preferable in the upper part of the building. 

Sectional forms are better and more economically constructed by build- 
ing them flat upon the ground than by constructing them in the position 
in which they are to be used. Care should be exercised to build them true 
and to have the face as free from irregularities as possible. The sheeting 
for the inside of the wall should be surfaced on the side next to the concrete, 
to give a smooth interior finish. 

The outer and inner form should be joined at the top by nailing cleats 
between the uprights, being careful to separate the forms the exact width 
of the wall. The forms should be united a short distance from the bottom 
by double wires, and should be separated at the same place by wood spac- 
ing blocks of a length equal to the thickness of the wall. When the spacing 
blocks are placed, the double wires are twisted by the use of a large nail, so 
that the outer and inner forms are firmly fastened together. They are sup- 
ported by securely bracing the inner form so that the wall will be plumb. 

If desired to provide the foundation with greater resistance to lateral 
pressure, or to afford a firmer base, " batter" in the wall may be secured by 
lengthening the spacing block which separates the outer and inner forms. 

Anchor bolts are embedded in the top of the concrete at suitable inter- 
vals for fastening the wall plate to the foundation. 

Cellar Floors 

The methods of building concrete walks are fully described in another 
lesson. The methods of building cellar floors are similar. To avoid repe- 
tition, only the points of dissimilarity will be stated here. 

Where the ground is firm and well drained, the subbase may be omitted 
and the concrete floor laid directly on the ground. 

Drainage should be provided, preferably toward the center of the floor. 
The top of the floor should be given grade enough that water accumulating 
from scrubbing or other causes will run off through a tile drain laid beneath 
the floor and communicating with a natural outlet. 

Where a basement floor is below the level of ground water, the floor 
should be laid in a single sheet instead of being divided into slabs. The 
concrete should be mixed in the proportions of 1:2:3, and the floor rein- 
forced in both directions with 34-inch rods 8 inches apart, or by wire mesh 
having an equal cross-sectional area of metal. 

38 



Entrances 

Outside entrances to cellars should be constructed by building, at right 
angles to the cellar wall, forms for side walls sloping from the top of the 
foundation down to the ground and from the cellar floor up to the top of 
the proposed stairway. If excavation is carefully done, the earth may 
usually be used for the outer form. By pouring one side wall at a time, 
and reversing the form by changing uprights to the other side of the sheet- 
ing, one form may be used for both sides of the entrance. The form for 
the steps may be built after the side walls are hard enough to remove the 
forms. After the desired measurements of tread and riser have been 
decided upon, the plan should be laid out on the side walls, cross-pieces 
wedged between them and secured by bracing. The concrete used in the 
construction of the base should be as wet as possible without flowing from 
one step to another. 

The J^-inch facing course of the risers may be placed either by using 
a thin metal partition or by plastering the mortar on the inside of the face 
form before placing the coarse, wet concrete. The wearing course of 
treads is placed as in sidewalk work, and should be finished by wooden 
float to a surface reasonably smooth but rough enough to afford a good 
foothold. 

Window-frames 

Closer joints will be secured under cellar windows if the frames are not 
placed until the concrete has hardened. Extreme care should be taken to 
have the opening true, thus simplifying the work of placing the frames and 
making the joints tight. 

Finish 

Concrete for cellar walls should be of such consistence that when poured 
into the forms it will settle to place by gravity. While the forms are being 
filled the coarser aggregate should be spaded away from the face of the 
wall, bringing the mortar next to the forms. The mixture recommended 
for foundations and basement walls, 1:3:5, provides an excess of mortar 
for this purpose. Spading is equally important on the interior and the 
exterior. On the interior it gives a more finished surface, and on the 
exterior it increases water-tightness. On the outside of the wall, above 
ground line, the plastic appearance which walls will have after forms are 
removed may be overcome by removing the surface film of mortar by 
brushing with a wire or a stiff fiber brush and washing the wall with the 
acid solution mentioned in the lesson "The Surface -Finish of Concrete." 

39 



Removal of Forms 

Not only the proportions of ingredients and consistence of concrete 
itself, but the weather conditions have marked influence upon the time of 
hardening. Consequently no definite rule can be given for removal of 
forms. Two to three weeks will suffice under average conditions. Where 
the earth is utilized for the outer form more time will be required than 
where both forms are of lumber. Too early removal spells failure, and 
judgment must be exercised. 

Block Foundation Walls 

Well-made concrete blocks are extensively used for foundation and 
cellar walls. For the latter purpose they possess the advantage of an 
interior air-space which helps to preserve an even temperature in the 
cellar. Care should be exercised that the blocks are well made of properly 
selected and proportioned materials, mixed wet enough so that the per- 
centage of porosity and absorption will be low. For both foundation and 
cellar walls blocks must invariably be laid in cement mortar mixed in the 
proportion of 1 sack of Portland cement to 2 cubic feet of sand, and the 
joints must be thoroughly filled. For the even and correct filling of joints, 
a templet or mortar gage may be obtained from the manufacturers of lead- 
ing block machines. 

Walls for Superstructures 

The recent statement that the annual fire loss of American farm build- 
ings equals one-fourth of their total cost should be sufficient argument for 
concrete — a material that will not burn. 

There are several methods of using concrete for the main portion of all 
classes of buildings. The most common forms of its application are con- 
crete block and monolithic walls. The concrete block is fully discussed 
in another lesson. Monolithic walls may be either plain or reinforced. 
The principal reason for reinforcing monolithic concrete walls is to prevent 
cracks from the expansion and contraction of the concrete caused by 
changes in temperature. All walls exceeding 12 feet in height should be 
protected by sufficient horizontal and vertical reinforcement, which should 
depend upon dimensions and design of the particular structure. It is 
seldom necessary to reinforce monolithic walls over 8 inches in thickness 
when less than 12 feet in height, except around window and door openings. 
One-quarter-inch rods should be placed from 1 inch to 2 inches back from 
the surface of the wall, and 2 inches from the angles of openings; three 
rods above and two on each side of the openings; two rods below windows; 
all projecting 10 inches beyond point of intersection. Diagonal rods 23^ feet 
long should be placed to pass intersections of horizontal and vertical rods. 

40 



The monolithic concrete wall lends itself more readily than any other 
type of building construction to the individual taste of the builder as to 
variety of design. In this respect it has no limitation except that of the 
builder's ingenuity in the construction of forms. Forms for walls above 
ground must necessarily be more carefully constructed than those for 
cellar work, as more perfect alinement is required and better surface finish 
desired. Home-made forms are, however, often used, being built from 
2-inch plank surfaced on one side, braced within and without and tied to- 
gether in the manner already described for cellar walls. In building walls 
above ground level continuous forms are sometimes used to avoid vertical 
joints. 

Several systems of clamps are now manufactured for constructing 
forms of 2-inch plank. They generally provide for courses 24 inches in 
height, the same form being moved upward as soon as the last course has 
hardened sufficiently, thus effecting a great saving in lumber, although 
requiring a little more time in building. 

Metal forms are now obtainable and are in use by numerous contractors. 
They are serviceable and satisfactory and may be rented by the individual 
user from many of the manufacturers. 

REFERENCES 

"Reinforced Concrete Construction," by George A. Hool. Published by McGraw-Hill 

Book Company, New York City. 
"Concrete Plain and Reinforced," by Taylor and Thompson. Published by John 

Wiley and Sons, New York City. 



VI. The Surface Finish of Concrete 

Concrete is a product resulting from scientifically combining certain 
ingredients to form a material useful in construction because of its own dis- 
tinctive merits and not because of its resemblance to any other natural or 
artificial product. When properly treated, it develops beauty; it is not 
the beauty of onyx, marble, or granite, but the beauty of concrete. If 
taken for what it is, rather than what it resembles, its qualities, uses, and 
advantages are found worthy of exhaustive research. 

Mortar Facing 

Whenever it is desired to secure a rich mortar surface, one of three 
methods is employed. A mortar mixed to the consistence of paste may be 
spread on the inside of the forms and the concrete filled in behind it and 
all tamped at one operation, to secure a good bond. A board or block of 

41 



the desired thickness may be inserted, the concrete filled in, and the board 
removed, leaving a space to be filled by the mortar, using in this case a 
slightly wetter mixture. The third method, and by far the most general 
practice, consists in using a partition of sheet iron or steel having angle 
iron attached to one side to gage the thickness of facing mortar. Handles 
are attached to the top so that, as the face mortar is placed in front first 
and the concrete behind, the partition is gradually moved upward. The 
use of a rich mortar is not so prevalent as it was in the earlier stage of the 
concrete industry, because, as will be explained, far more pleasing effects 
may now be secured by other methods. 

Spading 

Where a smooth concrete surface is desired, a spade or face cutter is 
used, which is forced down beside the forms while the concrete is being 
placed, forcing the coarse aggregate back and allowing the mortar to fill the 
spaces next to the forms, resulting in a surface as smooth as the face of the 
forms. 

Sand Rubbed Surfaces 

Probably the cheapest method of finishing a smooth concrete surface 
consists in removing the forms at the end of a period varying from six 
hours to three days, according to the weather conditions, and finishing the 
surface by the use of a plasterer's float or small board, using sand and 
plenty of water between the board and the wall to do the cutting. If this 
work is done ^t a time when the concrete is neither too green nor too hard, 
good results can be cheaply secured, as a laborer will in this manner cover 
100 square feet in an hour. This method of finishing is recommended for 
factory construction and the rear of apartment buildings, and in general 
for such walls as do not require special treatment. 

Experimentation 

Careful trials should be made before undertaking any artistic treat- 
ment upon actual construction work. The. possibilities and variations in 
this work are unlimited, and some methods of work are expensive. Conse- 
quently any one intending to attempt the construction of an artistic surface 
should first try out the proposed method on several small samples from 6 
to 12 inches square. 

The surface desired will determine the selection, gradation, and pro- 
portioning of the aggregate, and will also influence the consistence of the 
mixture. Some of the more common materials selected for aggregate will 
be limestone, granite, marble chips, and other stone and gravels and sands 
of various colors. 

42 



Whenever it is necessary to use expensive materials to obtain the sur- 
face finish desired, they are used only in the mixture applied as a facing for 
surfaces to be exposed. As a rule, the facing mixture varies from 1 to V/2 
inches in thickness, the remainder of the work being of ordinary concrete. 
However, both must be placed in the forms at the same time to insure a 
perfect bond and a solid mass. The third method, already described, for 
placing mortar on the face of concrete work is recommended in this con- 
nection; that is, the use of a partition of sheet iron or steel. As rich mortars 
always have a tendency to develop minute cracks, they should be avoided, 
so far as possible, and a mixture of 1 sack of Portland cement to 2 x /i 
cubic feet of aggregate is therefore recommended in the production of 
artistic concrete surfaces. The thickness of the facing material should 
not be less than one inch when fine aggregate is used, and whenever coarse 
aggregate is used it should be at least twice as thick as the greatest diameter 
of the largest aggregate used. 

Brushed Surfaces 

It is sometimes desirable to remove the plaster-like appearance of the 
concrete as it comes from the forms. One of the best methods of over- 
coming this is to remove the forms in about twelve hours (it being always 
understood that the time of removal is dependent upon the weather and the 
nature of the construction). As soon as the forms have been removed, if 
a brushed surface is desired, the concrete should be brushed while still 
green with a steel brush or one of stiff palmetto or other fiber bristles. A 
good brush may also be made by clamping together enough sheets of wire 
cloth to make a brush about four inches wide. If the concrete hardens so 
that the mortar cannot be brushed away from the coarse aggregate, the 
mortar may be softened by a solution of muriatic acid. After brushing, the 
work should be treated with an acid solution, and for this purpose, if 
standard Portland cement has been used, the solution should be one part of 
commercial muriatic acid to three parts of water. After the use of an acid 
solution the work should be washed immediately and thoroughly with clean 
water, as any acid remaining upon the face of the work will ultimately 
cause streaks and discoloration. 

The following materials are recommended as suitable aggregates for 
the production of desirable brushed surfaces, it being understood in using 
any of them for aggregates that the mixture is to be 1 sack of Portland 
cement to 2 x /i cubic feet of aggregate : 

Yellow marble screenings up to 34 inch; red granite screenings up to 
34 inch; black marble graded from J^ mc h to Yi inch; white marble graded 
from y% inch to Y2 inch; river or lake gravel graded from 34 inch to J/£ inch. 

43 



To secure economy, limestone may be substituted for white marble, and 
either black granite or trap-rock may be substituted for black marble. 

The above materials are merely suggestive of the possibilities of con- 
crete surfaces. Infinite variations may be made by substituting and com- 
bining materials, while if one takes trap-rock, red granite, and limestone, 
for instance, by merely increasing or diminishing the size of one or two of 
the ingredients it readily will be seen that a great many combinations may 
be effected, all of which will produce desirable surfaces for brushing. In 
general, fine aggregate will produce a comparatively smooth surface of uni- 
form color, while coarser aggregates will give greater irregularity in both 
surface and color, producing a somewhat rustic appearance. 

One of the chief advantages of finishing surfaces by brushing is the 
adaptability of this process to every class of concrete construction. Park 
benches, lawn vases, lamp-posts, and statuary of all kinds may be finished 
by this process as easily as buildings. 

Rubbed Surfaces 

Where it is desired to leave a smooth surface in the shape produced by 
the forms, but to obtain a more finished surface than possible by washing 
with a float under which sand is used for cutting, the concrete may be 
finished when it is at an age of from one to two days by removing the form 
and rubbing the surface with a brick and sand, natural stone, emery, or 
carborundum. 

Where it is desired to finish concrete in this manner the large pieces of 
aggregate should be spaded back from the forms so that the face will con- 
tain little or no coarse aggregate. If a mottled surface is desired, it may be 
produced by a mortar composed of one part of Portland cement and 2^ 
parts of white marble or limestone, either of which will rub to a very beauti- 
ful surface. While the rubbing is in process, a thin grout composed of one 
part of cement and one of sand should be applied and well rubbed in. The 
work should afterward be washed down with clean water. 

Dressed Surfaces 

When concrete has thoroughly hardened, it may be dressed in the same 
manner as natural stone, although the stone-cutter's tools require slight 
alterations to suit the need of the concrete. While this work is sometimes 
done upon concrete when it is two or three days old, the best results are 
obtained after it is about a month old. The great disadvantage of dress- 
ing concrete with a stone hammer at too early an age is that pieces of the 
aggregate will be knocked out from the cement mortar, leaving unsightly 
holes, while if left for a few weeks, they will become so thoroughly bonded 

44 



that they will break under the hammer and give a uniform surface, much 
the same as natural stone. 

For this purpose the best tool is a special form of bush hammer designed 
to dress concrete, the points on the face of which are farther apart and 
larger than on the regular stone-cutter's hammer. A three-pound hammer 
with four points is a good size for concrete work, although larger ones are 
frequently used. Another hammer which has been especially designed for 
dressing concrete is similar to a pick having five teeth on each end. This 
is made in two forms, one consisting of a steel head six inches long, beveled 
at both ends, the other being in the form of a central cast steel head to 
which steel plates are bolted. In the latter form the plates are removable, 
and when dull are replaced by sharp ones. Three-eighths inch crushed 
granite screenings were used for facing the exposed surface of the Connect- 
icut Avenue Bridge, Washington, D. C, and the finish was obtained by 
bush hammering. Very desirable exteriors may be produced by bush- 
hammered panels finished with 2-inch smooth borders, as shown on the 
Piqua Hosiery Company's Building, Piqua, Ohio, a replica of which was 
exhibited at the Cement Show in 1914. By using this method all trouble 
in finishing corners is eliminated, and the architectural design accentuated 
and improved. For finishing large surfaces a pneumatic hammer is used, 
and produces a very uniform finish, doing the work much more rapidly 
than where the tools are operated by hand. 

Sand Blast Surfacing 

Sand blast is frequently used for finishing concrete surfaces on large 
construction. It removes the plaster effect left by the forms and produces a 
granular finish. Sand blasting involves the erection of quite a large and ex- 
pensive machine, forcing sand grains from a nozle by pneumatic pressure 
and driving them against the surface of the wall with such violence that the 
sand cuts out the softer particles of the concrete against which it is thrown. 

Upon a dense and thoroughly hardened surface a J^-inch nozle may be 
used, but if the surface is not thoroughly hard, say two or three months 
old, it is better to use a }/£- or even J^-inch nozle. Crushed quartz or sharp 
silica sand should be used for sand blasting. If a }/i-mch. nozle be used, the 
sand should be screened through a No. 8 screen; if a 3^-inch nozle is used, 
the sand should be screened through a No. 12 screen. Concrete should 
never be subjected to sand blasting until it is at least one month old. A 
nozle pressure of from 50 to 80 pounds should be maintained. 

Colored Surfaces 

For artistic work the suggestions already made with reference to the 
selection, gradation, and mixing of aggregate will accomplish better results 

45 



than any process of artificial coloring which may be adopted. However, 
this paper would be incomplete if some information were not included re- 
garding the possibilities of producing artificially colored concrete work. 

The coloring-matter should never exceed 5 per cent, of the weight of 
the cement, and should be mixed with the dry cement before water is added. 
Nothing but mineral coloring-matter should be used, and the following 
table, taken from " Cement and Concrete," by L. C. Sabin, is generally 
accepted as the standard authority for amounts of different coloring- 
materials. 

COLORED MORTARS 

Colors Given to Portland Cement Mortars Containing Two Parts River Sand 

to One of Cement 





Weight of Coloring-matter Per Bag of Cement 


Dry Material Used 


- 








x /2 Pound 


1 Pound 


2 Pounds 


4 Pounds 


Lamp black 


Light slate 


Light gray 


Blue gray 


Dark blue 

slate 
Bright blue 


Prussian blue 


Light green 


Light blue 


Blue slate 




slate 


slate 




slate 


Ultramarine blue . . . 




Light blue 
slate 


Blue slate 


Bright blue 
slate 


Yellow ocher 


Light green 






Light buff 


Burnt umber 


Light pinkish 
slate 


Pinkish slate 


Dull lavender 
pink 


Chocolate 


Venetian red 


Slate, pink 
tinge 


Bright pinkish 
slate 


Light dull pink 


Dull pink 


Chattanooga iron ore 


Light pinkish 


Dull pink 


Light terra- 


Light brick 




slate 




cotta 


red 


Red iron ore 


Pinkish slate 


Dull pink 


Terra-cotta 


Light brick red 



There will be exceptional cases where it is necessary or desirable to 
color concrete surfaces after the work has been completed. For this 
purpose cement paint should be used, several brands of which are now 
manufactured in a limited number of colors by reputable companies. 

Designs 

There remains only one feature of concrete surfaces to be discussed, 
and that is the production of mosaics or pattern work. The plasticity of 
concrete makes it lend itself particularly to the reproduction of beautiful 
designs of all sorts, which may be secured in a variety of ways. For the 
more elaborate designs the pieces of marble, if that be the material selected, 
should be glued face down upon tough paper in the same manner in which 
floor tile are prepared for laying. This paper, with the design upon it, 
should be placed in the form, and the concrete filled in and thoroughly 
rammed to place. After the forms are removed and the concrete allowed 

46 



to harden, the paper should be removed by wetting; then clean the face 
of the finished design with the usual acid solution, 3 parts of water to 1 
part of commercial muriatic acid. 



VII. Cement Products 

L Concrete Blocks 

Historical 

The use of concrete blocks is of ancient origin, and although it is the 
purpose of this lesson to deal essentially with modern practice, it will be 
interesting to know that blocks of various forms and sizes composed of 
material similar to the concrete of to-day were used in many of the monu- 
mental works of the ancient world, and may still be seen in southern Europe, 
well preserved after the lapse of centuries. 

The introduction of concrete blocks in America was, like all other uses 
to which concrete has been adapted, coincident with the perfection of the 
rotary kiln and the consequent development of American Portland cement 
manufacture. Houses constructed of solid blocks or of blocks separated 
by metal anchors and thus forming a hollow wall may still be seen after a 
half-century of usefulness; but these are examples built in the infancy of an 
industry which began to come into its own only ten years ago. At that 
time the idea of making blocks in shapes designed for use in constructing 
hollow walls, to insure warmth in winter and coolness in summer, — blocks 
impervious to moisture and of such weight that they could be readily 
made and laid, — gained so strong a hold upon the popular mind that many 
people rushed into the manufacture of concrete blocks without adequate 
knowledge of the nature of cement or of the methods necessary to insure 
success in any branch of the concrete industry. Fortunately, these condi- 
tions have corrected themselves, and the elimination of the ignorant and 
unscrupulous block-maker will follow. To-day the concrete block industry 
stands upon a firm foundation of experience and reliability, the compara- 
tively new building material being one which, having proved its efficiency, 
has come to stay. 

Utility 

The fire-resisting qualities of concrete are sO well known that it is 
necessary only to call attention to the fact that the design of the concrete 
block excels all other forms of concrete in this respect (excepting double 
monolithic walls only), because of the vertical and horizontal air-spaces 

47 



within the wall, which so far prevent the transmission of heat that in 
numerous fires it has been observed by reputable witnesses that the exposure 
of one side of a well-built 12-inch concrete wall to an intense and prolonged 
heat did not even damage merchandise on the other side. Damage to the 
blocks themselves has usually amounted only to slight chipping, due to the 
dehydration of the outer part, or facing, often applied in making blocks. 

The same feature, namely, the non-conductivity of an interior air- 
space, results in a decided saving of fuel during the winter and increased 
comfort in summer, while it especially distinguishes the concrete block as 
the most suitable building material for tropical and semi-tropical climates. 

While it is not only possible, but commercially practicable, to make 
concrete blocks of water-tight texture, the interior air-space makes "assur- 
ance doubly sure" during protracted rainy spells, and effectually safe- 
guards from the sweating so objectionable in other types of construction. 
Wherever the type of block used affords a continuous horizontal and vertical 
air-space, as in two-piece walls, furring may be eliminated. 

Materials of Manufacture 

The first requisite to the manufacture of a good concrete block is suit- 
able materials. The concrete block is a composite product, and can be 
no better than its weakest ingredient. 

The fundamental requirement is high-grade Portland cement, which 
must be kept in dry storage until used. Cement which has become damp 
enough to harden must never be used in making concrete blocks. If pro- 
portioning is done by volume, the commercial sack of Portland cement may 
be accepted as one cubic foot. If, however, sacks are opened before pro- 
portioning, the cement increases in bulk so materially that it is necessary 
to proportion by weight. (A sack contains 94 pounds net.) 

Sand 

The sand used in the mortar of a concrete block should be silicious, 
coarse and clean. If screened from bank-run gravel, care should be exer- 
cised to see that it is free from animal or vegetable matter. If foreign 
substances are present, they should be removed by washing the sand. The 
selection of aggregates and methods of determining their suitability have 
been given in a previous lesson. 

Gravel or Broken Stone 

The coarse aggregate for concrete blocks should consist of gravel or 
broken stone. Choice between the two depends upon local availability 
and desired surface finish. Crusher-run broken stone should not be used 
until the dust has been screened out and the stone properly sized for pro- 

48 



portioning. Bank-run gravel must be screened and reproportioned before 
using. This point cannot be too strongly emphasized, as many failures 
are directly attributable to neglect of this requirement. Whether strength 
and density or economy and the saving of cement be the aim, the block- 
maker cannot afford to use unscreened bank-run gravel. 

So far as strength is concerned, it is impossible to make a concrete 
block stronger than the aggregate of which it is in part composed. The 
ultimate strength is demonstrated when a fractured block shows the cleav- 
age — and not the pulling apart — of the coarse aggregate. 

As to surface finish, the possible variations resulting from choice of 
aggregate are numerous. The granites, marbles, white quartz, and gravel 
of variegated colors are increasingly popular for exposed surfaces. For the 
main portion of the block, necessarily cheaper, limestone is in most local- 
ities the best available broken-stone aggregate. Sandstones are variable 
in strength, and the softer ones do not make good concrete blocks. Hard, 
clean gravel is often cheaper than broken stone and is equally desirable. 

Proportioning 

When the materials have been selected, the next step will be their 
proper proportioning, and for this purpose it is necessary to establish an 
arbitrary standard of sizes — the sand grains passing through a screen of 34- 
inch mesh, and gravel or broken stone passing a 1-inch ring and being 
retained on a sand screen. 

There are certain well-established scientific methods of determining 
voids and establishing definite proportions, which has been fully treated in 
a previous lesson. For the present it may be stated that under average 
normal conditions a mixture of 1 part Portland cement, 2 x /i parts of sand, 
and 4 parts of gravel or broken stone (expressed as 1 : 23^ : 4) has been found 
most satisfactory for the body or main portion of all blocks. If it is desired 
to face the block with a finer material, the richness will be increased in pro- 
portion to the elimination of coarse aggregate, but 1 : 1% is as rich as should 
be used for any face, while a 1 : 2 is better except in cases where decidedly 
fine texture, such as tooled and scrolled work, is desired. 

Mixing 

No matter how carefully the materials may be proportioned, good con- 
crete blocks cannot be obtained unless the mixing is properly and thoroughly 
done. For important work it is both safer and cheaper to use a power- 
driven mixer of standard make and known efficiency. However, where 
the proposed work is not extensive enough to warrant the installation of a 
mixer, equally good results can be obtained from painstaking hand mixing, 
using a water-tight platform, first spreading out the sand, then the cement, 
4 49 



mixing both together thoroughly, then adding the water and shoveling 
until the mortar is of uniform color; after this the coarse aggregate, which 
has first been thoroughly wetted, should be added, and the whole mass 
turned twice after its addition. 

Consistence 

The water used should be clean and used in such quantity that a me- 
dium wet mixture will result. By this is meant one that shows rather an 
excess of water, so that when a small portion of the mass is firmly pressed 
in the hand, several drops of water will be released from the concrete. 

No other consistence of mix is now recommended, because the dry mix 
resulted in almost certain failure and the flowing mix was commercially 
impracticable for small plants, on account of the large number of molds 
and the consequent expense of equipment required. 

Molds and Machines 

Blocks are made by tamping or pressing the concrete in molds designed 
for the purpose, and it is manifestly beyond the scope of this lesson to dis- 
cuss the various machines individually. The choice of a machine is, in 
the main, a matter of price, stability of construction, and minor details of 
operation. Most machines provide for a block of convenient size and 
weight, penetrated by cores which, when withdrawn, leave the hollow 
space which gives the concrete block its peculiar efficiency. The machines 
operated by pressure instead of tamping generally make the two-piece 
blocks; that is, the blocks do not extend entirely through the wall as do 
the tamped hollow blocks. Both processes — tamping and pressing — and 
both designs, hollow and two-piece blocks, are now accepted as good con- 
struction by engineers and architects, if the rules heretofore given relative 
to selection, proportioning, mixing, and consistence are observed. If they 
are disregarded, no machine can produce a concrete block which will be 
creditable to the maker or satisfactory to the user. 

Curing 

The curing of concrete blocks is a very important part of the manu- 
facturing process. The setting of cement, or its crystallization, is a chem- 
ical reaction, accelerated by heat and possible only in the presence of 
moisture. 

If cured by water, blocks should remain in a closed room for twenty- 
four hours, after which they may be stacked under a shed with open sides. 
Blocks require frequent sprinkling for two weeks, and are not ready for 
use until a month old. Moreover, their color is affected by the variation 
of moisture and heat caused by wind currents to which they are necessarily 

50 



subjected in the open-air curing shed. To overcome these objections and 
to shorten the curing period, we strongly urge, wherever possible, the 
construction of a closed steam-curing room, in which the blocks may be 
cured for forty-eight hours in a saturated atmosphere at a temperature of 
100° to 130° Fahrenheit. The time should be doubled in winter. Such 
curing will be more effective, as the blocks will develop greater strength 
in ten days than air-cured blocks will in twenty-eight days. The color will 
more closely approach uniformity, owing to the fact that each block thus 
receives the same treatment. The corners and facing of blocks will not 
be exposed to the usual injuries almost inseparably connected with setting 
green blocks in the yard. The saving of time and yard room is by no 
means an insignificant item. Steam curing makes it possible to operate 
the plant twelve months in the year. 

Building Construction 

The different manufacturers of concrete block machines have evolved 
designs for corner, jamb, and chimney blocks and other special members, 
according to the requirements of each particular system. These are gen- 
erally well adapted to their intended usages, but the block-maker must bear 
in mind that corners and jambs are subjected to greater wear and greater 
possibility of accident than are ''stretcher " blocks, and suffer more exposure 
in time of fire. Consequently they require special care in making and will 
cost proportionately more. Accessories, such as joist-hangers at floor 
levels and T-rods for securing roof plates, are manufactured by several 
reputable firms and are advertised in the columns of current concrete pub- 
lications. 

Footings should be of poured concrete in which the lower course of the 
foundation wall may be embedded. Concrete blocks 12 inches wide form 
an ideal cellar wall, this being ample thickness for the foundation wall of a 
two-story building. The walls of the first story may be of the same width, 
those of the second story reducing to 10 inches. Higher buildings will 
usually be constructed in cities or towns where thickness of walls is regulated 
by ordinance. 

Appearance 

The possible variations in surface finish of concrete blocks afford almost, 
unlimited opportunity to the block-maker who remembers that concrete 
is a separate and distinct building material, possessing possibilities beyond 
the range of those afforded by either brick or stone. If he grasps this fact, 
he will cease his efforts to produce a plastic and unpleasing counterfeit of 
the cheaper grades of stone work. He will learn that, by proper selection 
of aggregate, he can secure a surface which, left plain and smooth, is as 

51 



beautiful as a mosaic, or which, roughened by brushing a film of cement 
from the surface of a newly made block and washing the face so roughened 
with a 1:3 solution of commercial muriatic acid, will produce effects of 
startling originality and beauty. 

II. Concrete Fence Posts 

General Requirements 

What has been said in Section I of this lesson regarding the general 
principles of concrete construction will apply with equal force to concrete 
fence posts, and will not, therefore, require repetition. 

The concrete fence post, like the concrete block, is a comparatively 
small unit, manufactured for a particular purpose, and thoroughly seasoned 
before being put to its ultimate use. Consequently the same care must be 
exercised in the selection as well as in the proportioning and mixing of 
materials. 

Consistence 

Slightly more water is necessary in mixing concrete for fence posts than 
is used for blocks, owing to the different process of manufacture. A 
quaky mixture, which is wet enough to be just beyond the possibility of 
tamping, is used for posts — compactness in filling the molds being secured 
either by agitating the concrete by stirring or jarring the mold. 

Reinforcement 

In but one other respect does the concrete fence post depart from the 
process of manufacture applied to the concrete block. The peculiar duties 
demanded of the concrete fence post subject it to strains beyond the lateral 
resistance of a plain concrete member having such a small cross-section. 

To overcome the strains and thrusts peculiar to the duty demanded of 
the fence post reinforcing wires or rods of steel are introduced, and it is 
very important, both as regards the strength, of the post and the saving of 
material, that the reinforcement be properly placed. By imagining a post 
constructed of rubber and considering how such a post would act if bent 
far over to one side, the theory of reinforcement is easily pictured to the 
mind. A rubber post would manifestly be stretched on one side and 
pinched on the other, so we say that one side of the post will sustain tensile 
stress while the other will be subject to compression. As is well known, 
concrete is strong in compression and weak in tension, or resistance to 
pulling strains; hence on the side that is stretched we introduce just steel 
enough to balance or develop the opposing compressive strength of the 

52 



concrete. Thus we secure maximum efficiency from both the concrete and 
the steel. We are unable to tell in advance which of the four sides of a 
post will be called upon to withstand the thrust; therefore, we usually 
embed at each corner of the post, % inch from the surface, a J^-inch steel 
rod, twisted bar, or wire. In this way a direct load from any side is 
resisted by two rods acting in unison. 

Dimensions 

Posts are usually made 7 feet long, 3 inches square at the top, and 5 
inches square at the bottom, or they may be made 4 inches square at the 
top and 4 inches by 6 inches at the bottom. The dimensions first given 
are usually preferred, on account of the taper on all four sides making it 
very easy to fasten the line wire by merely tying a small wire to it and 
making it taut around the post. The method of making holes through 
posts is objectionable because of weakening the posts, and also because 
such holes establish an arbitrary place for fastening line wires which is fre- 
quently inconvenient and often interferes with uniformity in fence con- 
struction. The last-mentioned objection is also a fault of staple and T- 
shaped fastening devices of metal, which are, moreover, liable to failure 
from rusting on account of exposure to the weather. 

Molds 

The preparation of "knock-down" molds using head pieces and clamps 
— the lumber being protected from warping by painting with equal parts 
of boiled linseed oil and kerosene — is a very simple matter, and will cause 
no inconvenience to the ordinary manufacturer. However, if he has a 
large amount of fence to build, it will probably be more profitable for him 
to purchase a set of steel molds from one of several firms now manufactur- 
ing them in sets, known as "gang" molds, which permit making from 4 
to 12 posts at one operation. 

Whether a mold be made of steel or lumber, the essential points are 
that its sides shall be strong enough to remain true under the lateral pressure 
incident to filling the mold compactly, and that the mold be so constructed 
that the long, slender concrete post may remain undisturbed until it has 
attained sufficient rigidity to be removed without harm. This will usually 
require a week. No post should be used until it is a month old. 

Hence most molds are arranged to unclamp so as to be easily removed 
from the post, leaving it lying on the bottom board. While there are 
machines for making posts in vertical position, it will generally be found 
more practicable to make them horizontally, placing the reinforcement in 
the proper places while filling the mold. 

53 



Cost 

Under average conditions the cost of the materials used in a concrete 
post will be 23 cents. Scarcely anywhere can cedar, white oak, chestnut, 
or locust posts compete as to price, and when we consider the greater life 
of a concrete post due to immunity from fire, insects, and rot, we can easily 
understand its marvelous popularity. 

Corner Posts, etc. 

Corner posts are larger than line posts and require additional reinforce- 
ment. Eight by eight inches without taper, reinforced by four T 9 g-inch 
steel rods or other reinforcement of equal cross-section, makes a substantial 
corner post. 

Braces may be made in home-made molds 5 inches square and 10 feet 
long, with proper bevel at the end and four ^g-inch steel rods for reinforce- 
ment. Lugs may be cast on the corner posts to engage the braces, or a 
mortise made in the face of the corner post. 

On account of the small number required, gate posts will warrant addi- 
tional cost and should be plain but massive, thereby materially adding to 
the appearance of the fence and indirectly enhancing the value of the farm. 



VIII. Concrete Walks and Curbs 

I. Concrete Sidewalks 

Economy and Durability 

When compared with any other material suitable for sidewalks, the 
low cost and permanence of concrete have resulted in its almost uni- 
versal adoption, in enterprising communities. But it is essential that no 
one engage in the construction of anything so important as sidewalks are 
to the welfare of the community without thoroughly investigating the 
principles upon which success depends, and becoming entirely familiar 
with the best modern practice. 

One- and Two-course Walks 

In the early days of concrete walk construction it was the universal 
practice to use a base of lean concrete over which was spread a mortar 
top varying from % inch to 1 inch, made of cement and sand or cement and 
stone screenings. This top or wearing surface was usually troweled to a 
" glassy" surface, under the belief that a very smooth surface made a 
stronger appeal to the public eye. Very serious objections to this practice 

54 



have arisen. Not only has a surface so finished been found slippery and 
dangerous to pedestrians, especially in winter weather, but in cases of 
careless construction the imperfect bond between the top and base has 
resulted in the two separating, causing ultimate failure of the walk. 

In the one-course construction recently introduced a single mass or 
thickness of well-made concrete is used, and the surface, instead -of being 
troweled, is finished with a wooden or cork float, resulting in an even but 
not smooth tread, which overcomes the objection of the slippery troweled 
surface. Using one mixture throughout the walk, all of which is placed 
and tamped at one operation, does away with any possible line of cleavage 
or separation, consequently insuring absolute permanency, the entire slab 
being a homogeneous unit. 

Some sidewalk contractors still feel that a saving in cost may be effected 
by using a leaner concrete for the base. To correct this impression, data 
have been collected showing the comparative cost of one- and two-course 
walks. 

In one-course walks 4^ inches of the richer mixture is undoubtedly 
equal in strength to 5 inches of the two-course walk, using a leaner mixture 
for the base. 

The following table gives the cost of materials used in the construction 
of 100 square feet of sidewalk, and is based upon the following prices : 

Portland cement, $1.50 per barrel net; sand, $1.25 per cubic yard; 
gravel, $1.50 per cubic yard. (It should be understood that on account of 
freight on long hauls the cement will sometimes cost twice as much as 
shown.) 



5-inch two-course . . 
43^-inch one-course . 



Mixture 



1:2^:5 base) 
l:l^top I 
1:2:3 



Bbls. 
Cement 


Cu.Yds. 

Sand 


Cu. Yds. 
Gravel 


2.52 

2.42 


.80 
.73 


1.21 
1.08 



Total Cost, 
Materials 



56.79 
6.16 



Materials 

In the construction of concrete sidewalk, as in all other concrete con- 
struction, a standard brand of Portland cement should be used. 

Fine aggregate should consist of sand, crushed stone (free from dust), 
or gravel screenings, graded from fine to coarse and passing a screen of 
J4-inch mesh. It should be clean and free from foreign matter. On 
account of resistance to abrasion granite screenings have been used ex- 
tensively for the wearing surface where there is considerable traffic. 

Coarse aggregate should consist of clean, well-graded gravel or broken 

55 



stone, varying in size from 34 inch to Vyi inches. Bank-run gravel should 
never be used without screening and remixing in the proper proportions; 
it usually contains an excess of fine material, rendering proportions un- 
certain and indefinite. If the gravel contains loam, clay, or other for- 
eign matter, it should be washed before being used. 

Proportions 

In the construction of one-course walk the materials should be mixed 
in the proportions of 1 sack of Portland cement, 2 cubic feet of fine aggre- 
gate, and 3 cubic feet of coarse aggregate. 

In the construction of two-course walk the concrete for the base should 
be mixed in the proportions of 1 sack of Portland cement, 2^ cubic feet 
of fine aggregate, and 5 cubic feet of coarse aggregate. 

In two-course work the top, or wearing, surface should consist of mortar 
mixed in the proportions of 1 sack of Portland cement to not more than 2 
cubic feet of fine aggregate. 

Mixing 

The importance of thoroughly mixing the materials in the construc- 
tion of concrete sidewalk cannot be too strongly emphasized. Whenever 
possible, a power batch-mixer should be installed. On a contract of any 
considerable size power mixing will be cheaper than hand mixing, and every 
contractor has found the work of mixing by hand so laborious that the 
fatigue of the men has a marked effect upon the quality of the concrete. 

Concrete Mixers 

Batch mixers consist mainly of a rotating drum driven by steam, gaso- 
lene engine, or electric motor. Both the shape of the drum and the use of 
inside deflectors are relied upon to secure thorough mixing. The order in 
which the material is discharged from a batch mixer is independent of the 
order in which the materials are placed in the mixer. Hence all materials 
required for one batch are dumped into the mixer at one time, no attention 
being given to the order in which they are introduced. After the drum 
has made a few revolutions water in measured quantity should be added, 
and the mixing continued for a specified time or definite number of revolu- 
tions. A mixer must always be run slowly, to secure the best results. 

Continuous mixers consist mainly of a number of hoppers for the several 
materials, placed over one end of a semi-circular trough containing blades 
or vanes fixed to a rotating shaft. Motive power is generally supplied by 
a gasolene engine or an electric motor. Dry materials are fed automatic- 
ally from the hoppers into the trough, where water is added and the mass 
carried along by the blades to the discharge end. 

56 



Mixers of the batch type give better results, because the mixing is 
under the operator's control, and may be continued until the materials 
of each batch are perfectly mixed. Moreover, the measuring of materials 
can be regulated positively, whereas with continuous mixers variation in 
the amount of moisture in the sand, flufhness of the cement, or arching of 
material in the hoppers will vary the relative proportions of the different 
materials in the mixture. 

Consistence 

Concrete used for one-course walk should be wetter than a mixture 
used for the base of two-course walk, sufficient water being used to make 
a quaky consistence. Enough water should be added so that when the 
concrete is placed and lightly tamped the mortar will flush to the surface 
and make finishing easy. 

Mortar for the wearing surface of two-course walk should be mixed 
to such consistence that it will spread under a straight-edge resting on the 
forms, but should not be wet enough to cause excess water to stand on the 
surface after finishing with a wooden float. If surplus water appears on 
the top of the mortar, after floating, it must be taken up with a sponge or 
mop. The practice of throwing dry cement on a finished surface to take 
up surplus water should be condemned. 

Subgrade 

"Subgrade" is the term applied to the surface of natural soil as pre- 
pared to receive the subbase, or to receive the sidewalk directly where a 
subbase is unnecessary. The subgrade should not only be level, but should 
be practically uniform in density. If there are any holes or soft spots in 
the ground, they should be filled, and the filling be tamped. In the case of 
a fill the earth should be tamped in layers not exceeding 6 inches in thick- 
ness, which should extend at least one foot on each side of the walk, the 
sides having a slope of 1 to V/i. The subgrade should have a slope (toward 
the curb on city streets) of Yi inch to the foot, to allow for drainage, and 
should be 11 inches below the finished surface of the walk, except when no 
subbase is required, in which case the subgrade should be 5 inches (or 4^2 
inches) below the finished surface of the walk, depending on whether the 
walk is of two-course or one-course construction. 

Subbase 

The subbase is the foundation for the walk; it is laid on the subgrade, 
and is immediately underneath the concrete base. The subbase should 
consist of broken stone from which the fine particles have been removed 
by screening, coarse gravel, cinders, or blast furnace slag, the idea being to 

57 



secure a porous material through which water will readily drain. The 
subbase should be 6 inches in thickness, laid directly on the subgrade and 
thoroughly tamped. On fills, the subbase should be the full width of the 
fill, and the sides should have the same slope as the sides of the fill, namely, 
1 to 13^2- Wherever the climate is such that freezing occurs during the 
winter, the subbase is an essential part of concrete walk construction. 
Only where there is no danger of frost, or where there is perfect drainage, 
can the subbase be safely discarded and the concrete base be laid directly 
upon the subgrade. 

Forms 

Forms may be made from 2-inch lumber, the width being determined 
by the height of the walk, usually 4^ inches in the case of one-course 
walk and 5 inches in the case of two-course walk. Thirty-six square feet 
should be adopted as the maximum area of a single slab, and 6 feet as the 
greatest dimension permissible. Places where the cross-pieces join the 
side forms should, in two-course construction, be very plainly marked, so 
that when the wearing surface is laid, the final grooving may coincide 
with the joint in the base. Forms must be kept well cleaned and must not 
be used on a new job if concrete from the last job is sticking to their face. 
Several well-designed steel forms are now manufactured, which may be 
advantageously used whenever the area of walk to be constructed will 
justify the initial expenditure. Construction will be more uniform if such 
forms are used, and in the long run they will more than pay for themselves. 

Placing 

In constructing one-course walk the concrete should be placed and 
tamped to a thickness of 43^ inches. Steel tampers are used, varying 
from 6 by 6 to 10 by 10 inches. For the finishing of one-course walk a 
steel tamper with a face 8 inches square is preferable. A commercial 
type has pyramidal projections, which force the coarse aggregate below 
the surface, leaving the finer particles at the top, ready for finishing, with 
a wooden float; a steel trowel should never be used for finishing any walk. 

In constructing two-course walk the concrete should be placed and 
tamped to a depth of 4J4 inches, allowing % inch for the wearing surface, 
which will be mixed separately, and must be placed as rapidly as possible 
after the placing of the base. If any considerable time elapses between 
placing the base and laying the wearing surface thereon, the bond between 
the two will be in danger. 

Finishing of the wearing surface or face may be done in several ways, 
and while the use of a wooden float is always preferable, there are those 
who still wish the surface troweled. If troweling is done, it should be as 

58 



lightly as possible, in order to prevent the formation of fine cracks and 
checks as well as a glassy surface. 

The wearing surface should be cut through with a trowel directly over 
the joints in the base, and the groover run over the surface along the joint. 
Sides should be finished with an edger having a J/^-inch radius. 

If the laying of slabs is continuous, the cross-pieces should be removed 
when a slab has been completed, and the material for the next slab placed 
immediately. In order to insure perfect joints between slabs it is becom- 
ing quite common to construct slabs alternately. In this way the cross- 
pieces are allowed to remain until the cement has partially hardened before 
being removed and the material for adjoining slabs placed. In this 
manner the slabs form distinct units, and are not so likely to break in case 
of any future settlement in the foundation. The same result may be 
attained by using metal cross-pieces remaining in place until the concrete 
has partially hardened. 

Coloring 

If it is desired to vary the natural color, the use of lamp black, iron 
oxide, or any mineral coloring-matter is allowable, provided it is thoroughly 
mixed with the dry sand in quantities not exceeding 5 per cent, of the weight 
of the cement. Accuracy in measurement and thorough mixing are ex- 
tremely necessary if uniform color is to be expected. 

Protection 

As soon as the concrete has hardened sufficiently to prevent the sur- 
face from being pitted it should be sprinkled with clean water and kept wet 
for at least four days and not be exposed to traffic until thoroughly 
hardened. 

Freezing 

Under ordinary circumstances the construction of concrete walk dur- 
ing freezing weather is not advocated. If circumstances make it imperative 
to proceed with the work at such time, the requirements on all concrete 
work, such as heating the water and aggregates, must be observed, and 
precautions must be taken to protect the work from freezing for at least 
five days after placing the concrete. It is essential that both the sub- 
grade and the subbase should be free from frost when the walk is laid. 

Expansion Joints 

Expansion joints should be 50 feet apart and }/i inch wide. They 
should be filled with tar, prepared felt, or some other material which will 
retain elasticity under changing atmospheric conditions. 

59 



Precautions 

Walks should be grooved where crossed by driveways, and if a two- 
course walk, the wearing surface should be two inches in thickness at the 
driveway crossing. 

Where a new walk joins an old one and either the grade has been 
changed or the old walk was not properly laid to grade, lajdng an entire 
slab at the grade necessary to joint the two walks will avoid the unpleasant 
and dangerous beveling that is sometimes seen. 

In laying a walk around trees 6 inches clearance should be allowed to 
provide for future growth. The character of the trees should be investi- 
gated, as trees having lateral roots on or near the surface of the earth are 
almost certain to cause trouble at some time. 



II. Concrete Curb and Gutter Combined 

Combined curb and gutter is recommended only for streets which are 
not to be improved by permanent pavement. Where a street is merely 
graded or surfaced with disintegrated granite or some similar material, it 
is necessary to construct concrete gutter in connection with the curb. 

Similarity to Sidewalk Construction 

Concrete curb and gutter is closely associated with concrete sidewalk 
construction, not only on account of its position when placed, but because 
the materials and method of using them are much the same. 

What has already been said in this lesson in regard to cement selection 
of fine aggregate and selection of coarse aggregate for concrete sidewalk 
applies equally to concrete curb and gutter. 

Materials must be mixed with the utmost thoroughness, and a batch- 
mixer should be used whenever possible. If the mixing must be done by 
hand, it should be upon a water-tight platform, according to the best 
methods, which involve spreading the sand, then the cement, mixing them 
until of uniform color, incorporating the coarse aggregate, adding water, 
and turning the entire mass at least three times, or until of uniform con- 
sistence. 

As in the case of concrete sidewalk, concrete curb and gutter must be 
carefully protected after placing., and must be kept thoroughly wet for the 
first four days. 

Precautions must be taken, when necessary, to protect from frost for a 
period of five days, and both the subbase and subgrade must be entirely 
free from frost at the time of placing the concrete. 

The concrete should be mixed to a quaky consistence, so that water 

60 



will flush to the surface under slight tamping. Mortar for the wearing 
course must be of such consistence that it wall not require tamping, but 
can be easily spread into position. 

All the above requirements are substantially the same as for the con- 
struction of concrete sidewalk. 

Subgrade 

The subgrade must be level, firm, and free from soft places. If filled, 
the earth must be tamped in layers not exceeding 6 inches in thickness. 
Whether a fill or an excavation, the surface must be finished 1 1 inches below 
the established grade of the gutter. 

Subbase 

Upon the subgrade must be laid the subbase consisting of suitable 
porous material, such as slag, cinders, large gravel, or broken stone, from 
which the finer pieces have been screened, and this material must be 
thoroughly compacted and rolled to a thickness of 5 inches, so that its 
surface will be 6 inches below the established grade of the gutter. The 
above measurements are given with reference to the grade of the gutter, 
which is itself 6 inches below the grade of the curb. 

Construction 

In combined curb and gutter, the depth of the back will be 12 inches, 
the depth of the face 6 inches, the breadth of the gutter from 16 inches to 24 
inches, and the sections from 5 feet to 8 feet in length, with }/o hich expan- 
sion joints occurring every 150 feet. Expansion joints should be filled 
with tar, prepared felt, or other suitable material which will retain elasticity 
under changes of temperature, and the abutting corners should be rounded. 
The necessity for liberal expansion joints between the curb and the side- 
walk deserves especial emphasis, as cases of concrete curb and gutter failing 
through lateral pressure from expanding sidewalk are numerous and un- 
necessary. 

Two-inch lumber may be used for forms, except at street corners, where 
the radius should not be less than 6 feet, and may be provided for by sub- 
stituting metal strips in place of the usual lumber. Metal cross-pieces 
must be provided between sections, and their position distinctly marked 
upon the front and back pieces of the forms in order that the wearing 
course, when applied, may be cut through and grooved exactly above the 
joint in the concrete base. The slope of the gutter may be regulated and 
maintained by using an ordinary wooden level with a nail driven in the 
bottom at one end, and extending out a distance equal to the required pitch. 

61 



The street side of the gutter will be raised at the approach to street-cross- 
ings, so that it may conform to the grade at the sidewalk crossing. 

A number of very satisfactory varieties of forms are now manufactured 
from sheet steel. They are not only more durable than wood, but are 
held in place by templets, which do away with the necessity of cross-pieces 
and eliminate the clamps required in connection with wooden forms to 
hold in place the board forming the face of the curb. This is a distinct 
advantage, affording considerable saving of time, while the templets 
themselves satisfactorily divide the finished curb and gutter into sections, 
which is a point of considerable importance in view of the disaster which 
might otherwise follow a foundation failure. 

Placing 

In the construction of two-course concrete curb and gutter the concrete 
should be mixed in proportions of 1 sack of Portland cement, 2J/2 cubic 
feet of fine aggregate, and 5 cubic feet of coarse aggregate. Mortar for 
the wearing course should be mixed in the proportion of 1 sack of Portland 
cement to 2 cubic feet of sand or other suitable fine aggregate. 

Concrete mixed in the proportions above specified should be deposited 
in the forms and thoroughly rammed to place, allowing %-inch for wearing 
surface, the latter to be applied as quickly as possible in order to secure 
an effective bond between the base and the wearing surface. 

Three different methods of applying the wearing surface have been 
used. The first consists in applying the mortar to the top of the gutter 
and the top of the curb, and as soon as these have been finished, removing 
the form from the face of the curb and troweling the mortar down the 
vertical face. This method is unsatisfactory for several reasons. It often 
results in the face of the curb being but thinly covered, it necessitates the 
use of too dry a mixture on the vertical face, and results in excessive trowel- 
ing which develops hair cracks and checking on the wearing surface. The 
second method consists in plastering on the inside of that portion of the 
form making the vertical face or street side of the gutter % inch of plastic 
mortar, the form being filled with concrete at the same time, so that the 
introduction of the mortar and concrete is practically simultaneous. 
When the form lacks % inch of being filled, the top is then filled with 
mortar. After removing the forms, the only work remaining is the fin- 
ishing of corners. A lj^-inch radius is given to the curb on the street side 
and the intersection of the curb and gutter; all other edges are rounded to 
a ^g-inch radius unless protected by metal. The third method differs from 
the second only in slipping a 1-inch board, 6 inches wide and surfaced on 
one side, inside of that portion of the form making the face of the curb. 
When the form has been filled with concrete this board is withdrawn, and 

62 



the space left by its withdrawal is then filled with plastic mortar. The 
second method will usually secure a better bond between the base and the 
wearing surface. 

Excessive troweling is too often practised in finishing the wearing sur- 
face of concrete curb and gutter. A large part of the finishing may be 
better accomplished by the use of a stiff fiber brush which will give a 
more durable surface, less likely to develop hair-cracks and checking. 

One-course Work 

Concrete curb and gutter has not yet been so extensively constructed 
after the one-course method as has one-course sidewalk, but one-course 
construction is likely ultimately to supersede, to a great extent, two- 
course, on account of greater durability, more permanent wearing surface, 
and the saving in time and labor. In one-course work the concrete should 
be prepared in proportions of 1 sack of Portland cement, 2 cubic feet of 
fine aggregate, and 3 cubic feet of coarse aggregate, using a tamper with 
pyramidal or similarly formed projections that will drive the coarse aggre- 
gate below the surface and leave the mortar on top for finishing with a 
wooden float. 



III. Concrete Curb 

In all cases where there is a probability of permanent road improvement 
concrete curb should be constructed without gutter, as the gutter will be 
provided by the slope of pavement adjoining the curb. By this method 
of construction the longitudinal joint separating the pavement from the 
curb is at the extreme edge of the pavement, and the objectionable longi- 
tudinal joint between pavement and gutter is eliminated. 

Building concrete curb without gutter is very simple. There is no 
occasion for making the wearing surface richer than the main body of 
concrete; consequently the entire curb should be of 1:2:3 concrete finished 
with a wooden float, as recommended for one-course curb and gutter work. 

For constructing concrete curb without gutter, the subgrade should be 
finished 30 inches below the established grade of the work. The subbase 
should occupy 6 inches, making its surface 24 inches below the established 
grade of the curb. Concrete curb should be 12 inches wide at the base, 
6 inches wide at the top, 24 inches high, and have a batter on the street 
side of 1 to 4. 



63 



Laboratory Guide for an Elementary Course in 

Concrete Work 

To aid instructors in planning and conducting an elementary course in 
concrete construction, the Association of American Portland Cement 
Manufacturers has prepared the outlines and suggested exercises which 
follow. As the course is now being given in a number of schools, four hours 
per week for thirty-six weeks are devoted to this work; but by condensing 
the outline and omitting some of the laboratory exercises, the time may be 
decreased about one-half, without entirely omitting any of the essentials 
of elementary theory and practice. An effort has been made to present 
the work in a logical progressive order, but the arrangement may be al- 
tered as seems necessary to meet particular requirements. 

Scope of the Course 

This course may be considered as divisible into four parts : 

1. Class-room work, consisting of lectures and recitations. 

2. Sketching and drawing. 

3. Building forms and equipment. 

4. Preparing, placing, curing, and testing the concrete. 

What proportion of the total time available is to be given to each of 
these divisions will depend largely upon the features that the instructor 
desires to emphasize most; but in cases where the time available will not 
permit due attention to all parts of the work, sketching, drawing, and form 
building should be sacrificed rather than class-room work and practice in 
concreting. 

In concreting courses of this kind now being taught elsewhere, about 
one-half of the total time is devoted to lectures, " shop talks," and recitations, 
these preceding the other work under each division head in the outline. 

General Notes 

Many instructors have found that the best results can be obtained by 
separating the class into groups of from three to six pupils. Articles to be 
made are classified in groups, and each student is given a choice of several 
exercises in each group. When a group of students has forms ready to fill 
and has calculated quantities of materials needed, one large batch of con- 
crete is mixed by the group, from which all the forms are filled. This af- 
fords the students better practice than if each one were allowed to mix up 
only enough for some small flower-box or other exercise, although each stu- 
dent may mix his own batch when making test specimens. 

Greater interest is likely to result if it is possible to make short trips of 
inspection to some practical concrete work in process. Saturday afternoons 

64 



may well be taken up in this way, and the student given an opportunity to 
observe concrete work as it is carried on in actual practice, and have his 
attention called to examples of good and poor work. Local contractors and 
their foremen are generally quite willing to answer questions and explain 
their methods. 

Most of the following exercises can be used in farm mechanics work, 
as well as in manual training courses. The primary object is to teach the 
elementary principles of concrete construction, and this must be borne in 
mind in the selection of exercises. At the start, simple and useful articles, 
instead of more elaborate pieces, are to be preferred, but as the course pro- 
ceeds more complicated work may be undertaken. Artistic possibilities 
are limited only by the ingenuity of the students in designing and construct- 
ing the necessary forms. 

Suggested Laboratory Instructions 

Report on Laboratory Exercises 

A written report should be required from each student for each exercise 
assigned. Students should provide themselves with note-books in which 
all data should be recorded. No credit should be given for reports not 
based upon the original data taken in the laboratory and entered in the 
laboratory note-book. Reports should be written in ink. 

Reports should be turned in not later than one week after the exercise 
has been completed, and should be returned for corrections one week later. 
The form of report given below is suggested: 

Report Sbeet 

Name Date 

Title : : 

Object 

Hours' time spent on exercise 

Apparatus used 



Method of performing experiments. 

Conclusions 

5 65 



The drawings, descriptions, tables, and all calculations, together with 
answers to questions, should accompany the report sheet. 

Suggested Exercises for Elementary Course in Concrete 

Construction 

To be designed by the student: 

1. Building blocks. 

2. Horse block. 

3. Duck pond. 

4. Bird bath. 

5. Concrete foundation. 

6. Hotbed frame. 

7. Small trough. 

8. Rain barrel. 

9. Stock tank. 

10. Fish aquarium. 

11. Outdoor swimming pool. 

12. Ice-box. 

13. Greenhouse. 

14. Fence-posts. 

15. Hitching-post. 

16. Sun-dial. 

17. Flower-box. 

18. Garden-seat. 

19. Lawn pedestal for flower urn. 

20. Sidewalk tiles. 

Equipment Required 

In a number of schools a portion of the basement has been used for the 
concrete laboratory, but the room selected should have plenty of light and 
a smooth, level floor. Much of the work will naturally be done in the 
class-room and woodshop. Most of the following equipment can be made 
by the students in the woodshop classes: 

1. A well-made mixing platform. It will be cheaper to build a good one 
at the outset than to waste time and money in constructing and using tem- 
porary ones. A suitable platform can be built of 2-inch lumber nailed 
upon three 4 by 4's rounded at the ends. The platform should have a 
surface at least 12 by 7 feet. The outside 4 by 4's project 6 inches at both 
ends of the platform, and are bored for clevis irons so that the platform 
may readily be dragged about. 

66 



BILL OF LUMBER FOR MIXING PLATFORM 

12 pieces, 2 by 12 inch by 7 feet, dressed on one side and two edges (tongued 
and grooved preferred). 
2 pieces, 2 by 2 inch by 12 feet, dressed on one side and two edges. 
2 pieces, 4 by 4 inch by 13 feet, rough. 
1 piece, 4 by 4 inch by 12 feet, rough. 

2. Three measuring boxes holding 1 cubic foot, Yi cubic foot, and J4 
cubic foot, respectively, and preferably cubical in shape. 

3. Two wood trowels, 4 by 8 inches, Yi mcn thick. (See Plate No. 9.) 

4. Tamper. (See Plate No. 9.) A tamper weighing between 15 and 
20 pounds will be found suitable for school purposes. If made of pine, 8 
by 8 by 12 inches or 8 by 8 by 18 inches is to be recommended, or if make 
of oak, 8 by 8 by 8 inches, would weigh approximately 20 pounds. A 
straight handle made of l^-inch galvanized pipe or wood will suffice. 

5. Four small open bins for storing unscreened sand and gravel, 
crushed stone, screened gravel, and screened sand. (As only small quanti- 
ties of aggregates will probably be kept on hand at any one time, the bins 
need hold only about Yi cubic yard.) 

6. Water barrel. 

7. Two or three water-buckets. 

8. Wheelbarrow. (Preferably with a metal body.) 

9. Two or more square-nosed shovels. 

10. Screen for separating sand and gravel. (The best type of screen 
has longitudinal wires spaced % m °h apart, with horizontal wires 4 to 6 
inches apart to act as stiffeners. Common j^-inch square mesh will be 
found satisfactory, however.) 

11. Curing tubs for exercises. (Such tubs can be made from oak oil 
barrels sawed in two.) Old turpentine barrels should not be used, the 
turpentine preventing the setting of the mortar or concrete. 



Outline of the Course 

I. Materials and Mixtures 

1. Classroom Work. 

(a) Cement, its qualities and how to handle and store it. 

References : 

" Lessons in Concrete," No. 1. 

Bulletin No. 26, " Concrete in the Country," published by 
the Association of American Portland Cement Manufac- 
turers. 

General Notes: 

The history of Portland cement and the details of its manu- 
facture are interesting subjects to all, as is the matter of 

67 



testing Portland cement to determine its fitness for our pur- 
poses. On the other hand, it must be remembered that a 
thorough knowledge of how to employ cement for our various 
purposes is much more important than a knowledge of its 
origin, and that tests on cement, unless conducted under 
standard laboratory conditions and by competent cement 
testers, are not reliable and mean but little. 

Portland cement of any standard brand may be used without 
question, provided it has not been allowed to become lumpy 
in storage. In opening a sack it is well to run the hand down 
the inside in search of lumps. If there are particles present 
which will not crumble under the pressure of the fingers, the 
cement is unsuited for general use, although there may be no 
serious objection to using it in large foundations or other 
mass work after lumps have been screened out. 

(b) Sand, gravel, and stone. 

References : 

" Lessons in Concrete/ ' No. 2. 

Bulletin No. 26, " Concrete in the Country." 

General Notes: 

The definitions of the common materials used in the work 
should be made clear to the students. 

The term "aggregates" refers to sand, gravel, and stone for 
either mortar or concrete. 

11 Fine aggregate 1 '' is defined as "sand or crushed stone that 
will pass a No. 4 sieve; that is, a screen having four meshes 
to the linear inch." 

u Coarse aggregate" is material such as "gravel and crushed 
stone that is retained on a No. 4 sieve." The largest par- 
ticles in the coarse aggregate should never be larger than one- 
half the distance between the forms. 

"Bank-run gravel" is the term applied to gravel and sand 
just as it is taken from the pit, without being washed or 
screened. 

(c) Preparation, screening, washing, proportioning, and mixing. 

References : 

"Lessons in Concrete," No. 3. 

Editorial, "Engineering Record," May 30, 1914. 

"The Folly of Using Bank-run Mixtures in Concrete." 

General Notes: 
Screening. — Bank-run gravel should never be used as it comes 
from the deposit, but should be screened and then recombined 
in the proper proportions. Strong, dense, water-tight con- 
crete requires strict attention to proportioning. This pre- 
cludes the possibility of using bank-run material without 
screening. 

68 



Water Used. — Water used must be clean, free from oil, acid, 
alkali, and vegetable matter. 

Proportioning. — In proportioning by volume, a sack of cement 
is considered as one cubic foot, and by weight, a sack of 
cement may be accepted as 94 pounds net. Materials 
should always be carefully measured, never guessed at. On 
large jobs it is customary to measure aggregates in multiples 
of " one-sack batches." One cubic foot, the sack of cement, 
is taken as the unit of measure. The aggregates are then pro- 
portioned with suitable sizes of measuring boxes varying in 
capacity from 1 to 3 cubic feet. 

(d) Theory of mortar and concrete. 
References : 

Bulletin No. 26, " Concrete in the Country," p. 11. 

General Notes: 
The aggregates consisting of sand and gravel or broken stone 
are wholly inert until combined with Portland cement. 
Consequently, it is of prime importance that every grain of 
sand be enclosed in a film of cement and water and every 
piece of coarse aggregate be surrounded with cement mortar. 

The following table will be found very useful in calculating 
the quantities of sand and gravel, or stone, required for a one- 
bag batch of mortar or concrete, and in computing the vol- 
ume of the resulting mortar or concrete. 



TABLE NO. 1 



Mixtures 


Materials 


Vol. in 


Cu. Ft. 


Cement 


Sand 


Gravel or 
Stone 


Cement in 
Sacks 


Sand 
Cu. Ft. 


Gravel or 
. Stone 
Cu. Ft. 


Mortar 


Concrete 




1.5 




1 


1.5 




1.75 






2.0 




1 


2.0 




2.1 






2.5 




1 


2.5 




2.5 






3.0 






3.0 




2.8 






1.5 


3 




1.5 


3 




3.5 




2.0 


3 




2.0 


3 




3.9 




2.0 


4 




2.0 


4 




4.5 




2.5 


4 




2.5 


4 




4.8 




2.5 


5 




2.5 


5 




5.4 




3.0 


5 




3.0 


5 




5.8 



69 



TABLE NO. 2 

QUANTITIES OF CEMENT, SAND, AND GRAVEL OR STONE REQUIRED 
FOR ONE CUBIC YARD OF COMPACT MORTAR OR CONCRETE 



Mixtures 


Quantities of Materials 










Sand 


Stone or Gravel 




Sand 


Gravel or 
Stone 


Cement in 
Sacks 








Cement 


















Cu. Ft. 


Cu. Yd. 


Cu. Ft. 


Cu. Yd. 


1 


1.5 




15.5 


23.2 


0.86 






1 


2.0 




12.8 


25.6 


0.95 






1 


2.5 




11.0 


27.5 


1.02 






1 


3.0 




9.6 


28.8 


1.07 






1 


1.5 


3 


7.6 


11.4 


0.42 


22.8 


0.85 


1 


2.0 


3 


7.0 


14.0 


0.52 


21.0 


0.78 


1 


2.0 


4 


6.0 


12.0 


0.44 


24.0 


0.89 


1 


2.5 


4 


5.6 


14.0 


0.52 


22.4 


0.83 


1 


2.5 


5 


5.0 


12.5 


0.46 


25.0 


0.92 


1 


3.0 


5 


4.6 


13.8 


0.51 


23.0 


0.85 



Stone and gravel = 45 per cent, voids (average). 

1 sack cement = 1 cu. ft.; 4 sacks = 1 bbl. 

Based on tables in "Concrete, Plain and Reinforced," by Taylor & Thompson. 

It is necessary occasionally to mix up quantities of concrete or mortar 
requiring less than a sack of cement, and for small exercises some other 
unit of proportioning than the cubic foot is necessary. A quart measure, 
which holds approximately 2^ pounds of cement, or a peck measure, which 
holds approximately 22 pounds, will be found very convenient for measur- 
ing small quantities of cement. When dumped from the sack, cement 
becomes fluffy and occupies more space than when compacted in a sack; 
hence in measuring cement by volume it will be found necessary to jar it 
down a few times in the measure in order to get accurate results. Both 
coarse and fine aggregate can be measured by means of small measuring 
boxes holding J^, J^, and 1 cubic foot respectively; or by the quart or peck 
measure referred to above. 





TABLE NO. 


3 






1 sack cement 94 lbs. 2 cu. ft 




47 ' 


1 1 ' 




1:2 , 


32 ' 


% ' 




Mixture 


23.5 ' 


V2 ' 






16 ' 


Vs ' 






12 < 


H ' 






• 1 sack cement 94 ' 


3 ' 






47 ' 


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1:3 


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ixture 


23.5 ' 


% ' 






16 ' 


V2 ' 






I 8 < 


H ' 





sand 



Mixing 

The first step in mixing is to spread the sand in a thin layer over the 
center of the mixing platform, then spread the cement on top of the sand 

70 



and mix together dry, continuing the turning until the color is uniform and 
without streaks. After the cement-sand mixture has been turned at least 
twice it should be spread in a thin layer and the measuring box placed upon 
it. The proper amount of screened gravel should then be shoveled into the 
box and the latter lifted off. Mixing is then continued until the gravel is 
thoroughly distributed throughout the mass; this will require turning the 
batch at least twice. Water is then added slowly from a sprinkling can or 
from a small stream applied by a hose, the mixing continued until all parts 
of the mass are the same in color and consistence and wet enough so that 
there is a tendency to flatten out when the mass is heaped up. The con- 
crete must always be used within twenty minutes or half an hour after the 
water has been added. 

The quality of the concrete depends largely upon the amount of water 
in the mixture, a mixture such as described giving better results than a dry 
one; in fact, a dry mixture is not capable of developing all the strength of 
the cement. Mixtures containing less water are frequently used in making 
cement products, but the practice is a bad one and should be avoided when- 
ever possible. Too much water is likely to cause pockets and imperfec- 
tions in the surface of the work, and increases shrinkage while hardening. 

II. Forms and Molds 

1. Class-room Work. (Using slides or charts.) 

(a) Materials for making. 

References : 

" Lessons in Concrete," No. 4. 

Bulletin No. 26, " Concrete in the Country." 

Bulletin No. 23, " Concrete Tanks." 

General Notes: 

Forms are made of wood, metal, and combinations of wood 
and metal. 

(b) Various types. 

References : 
Same as those given under (a). 

General Notes: 

Various types of forms. 

1. Rectangular forms wholly of lumber. 

2. Rectangular forms using metal fastening. 

3. Rectangular metal forms. 

4. Circular forms of wood and sheet metal. 

5. Circular forms wholly metal. 

6. Miscellaneous. 

(c) General requirements, care, and use. 

References : 

Same as those given under (a). 

General Notes: 
Green lumber will keep its shape better in all rectangular 
forms than will lumber that is thoroughly dry. If dry lum- 

71 




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ber is used, it should be thoroughly wet before the concrete is 
placed. White pine is considered the best lumber for forms, 
although spruce, fir, and Norway pine are often used. The 
face of the forms should be free from knots, slivers, or other 
irregularities. The forms should be thoroughly cleaned each 
time they are used, so that no dry concrete is left sticking to 
the face of the forms. The use of oil or grease on the face of 
forms is recommended, as it prevents absorption of water 
from concrete and makes form removal easier. A mixture 
of equal parts of boiled linseed oil and kerosene is generally 
used for painting the forms. Tallow or animal fats should 
not be used in painting the forms. 

2. Form Work. 

Construction, small wooden molds for making test specimens. 

Exercise I-A 

Gang Mold for Test Specimens 

(Plates Nos. 1 and 2) 

The construction of a small wooden gang mold for making test 
specimens V/2 inches square and 6 inches long. 

Tools used: Saw, plane, square, gauge and hammer. 

MILL BILL OF MATERIAL FOR GANG MOLD 

4 pieces 1 inch x 3 inches x 12 inches S3S, base of form. 

2 pieces % inch x 13^ inches x 103^ inches S2S, sides of form. 

2 pieces % inch x \ x /i inches x 8 inches S2S, sides of form. 

4 pieces 34 inch x 13^2 inches x 63^ inches S4S, movable partitions. 

2 pieces 2 inches x 2 inches x 12 inches SIS, bottom strips. 

2 pieces 2 inches x 1 3^ inches x 3 inches S4S, blocks. 

2 pieces 2 inches x 13^ inches x 5 inches S4S, wedges. 

(See " General Notes" for instructions to be followed in selecting 
the lumber for wooden forms.) 

The joints of the mold should be as tight as possible. This will 
require care and accuracy in squaring up the various pieces before 
they are assembled. 

As shown in the assembled drawing of the small gang mold, the first 
thing to consider would be the base of the form, which will be made 
either of four 1 by 3 inch strips or two 1 by 6 inch boards held in 
place by 2-inch strips which can be made by cutting 2 by 4's length- 
wise. All pieces should be squared up and surfaced with a plane 
before they are put together. 

The sides of the form can be made from strips 1 inch thick and 2 
inches wide, planed down to z /± inch thick by V/2 inches wide and 
supplied with grooves as shown. The four movable partitions are 
made from 34" mcn stock, and the ends are slightly tapered so that 
they can be moved in their respective grooves without difficulty. 

Two of the sides of the form are fastened securely to the base by 
means of screws, and the other two sides are held in position by 

73 



means of wedges, which can easily be made by sawing a block in two 
diagonally. After all the pieces have been approved by the in- 
structor and the form has been assembled, the faces which will 
come in contact with the concrete should be given two coats of 
shellac. 











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Plate 2. — Details of Form for Test Specimens. 



Exercise I-B (Optional with Exercise I-A) 

Gang Mold for Test Specimen 

(Plate No. 3) 

The construction of this gang mold is much more simple than that 
described in Exercise I-A, and is preferable for work with younger 

74 




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boys. As shown on the plate, it is only necessary to cut and 
plane to size four strips 1J^ by lj^ by 12 inches and six blocks 1}4 
by 1H by 3 inches. One of the longer strips is fastened securely in 
position by means of three screws; all other parts of the mold are 
movable except the blocks that hold the wedges. The form is 
designed for molding three test specimens of the same size as those 
made in mold I- A. 

III. Tools and Equipment 

1. Class-room Work. (Using slides and charts.) 

(a) List of the common tools. 

Reference : 
Bulletin No. 26, " Concrete in the Country." 

General Notes: 

Common Tools. — Shovels, pails, tamper, float, edger trowel, 
groover, and' straightedge. 

Equipment. — Screen, mixing platform, measuring box, wheel- 
barrow, water barrel. 

(b) Directions for constructing floats, wooden trowels, tampers, 
straightedge, mixing platform, 'and mixing box. 

Reference : 
Bulletin No. 26, " Concrete in the Country." 

General Notes: 

For size, see accompanying drawings and general directions. 
Blackboard sketches will be found helpful in explaining the 
various tools and equipment. 

2. Woodshop Work. 

(a) Making a straight edge, float, wood trowel, measuring box, 
tamper, etc. 

Exercise 2-A 
A Device for Testing Small Concrete Specimens 

(Plate No. 4) 

This simple device for testing small concrete specimens can 
easily be made by elementary manual training students. It is 
intended for use only in testing very small beam specimens, 
and even for such work much more satisfactory results can be 
accomplished by the use of the home-made testing machine 
shown in Plates Nos. 5 and 6. 

The testing device consists of two triangular pieces of hardwood 
18 inches long, which can be clamped to any ordinary bench or 
table. The distance apart will, of course, depend upon the 
length of the specimens to be tested. The specimen should 
bear on the points at a distance of about Y2 inch from each end, 
and the triangular supports should always be kept exactly 
parallel. 

76 




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The loads are applied by adding sand or water, preferably the 
former, to a pail suspended by a hook secured to a third tri- 
angular piece or saddle resting across the specimen at the center. 
Sand used should be fine and thoroughly dry, so it will readily 
flow through a small rubber tube connected to a can or funnel, 
the flow being shut off by a pinch-cock fitted to the tube. 

Exercise 2-B 
Testing Machine 

(Plates Nos. 5 and 6) 

This small, home-made machine was designed by the Muncie 
(Indiana) Normal Institute for testing specimens either 1 by 
1 by 12 inches or 1 by 2 by 12 inches. 

It consists of levers so arranged that the load applied to the 
specimen is increased ten times over that applied to the ma- 
chine. It is equipped with an automatic cutoff, which prevents 
the load from increasing after the specimen has failed. 

The frame which supports the machine can be made of pine, 
but the lever arms should be of hard wood. One end of the 
lower lever supports a can, which is located just below another 
can containing a supply of dry sand. At the other end of the 
lever a ball weight is suspended which can be adjusted so as to 
balance the levers just before the test is applied. 

At the center of the bottom of the can containing the sand is a 
3/2-inch hole through which the sand is allowed to flow into the 
lower box. An automatic cutoff controlled by a coiled spring 
and trigger is provided. A No. 9 wire is attached to the lower 
lever and projects through a small opening in the cutoff, when 
the large hole in cutoff is directly under the opening in the sand 
supply can. This wire acts as a trigger, and as the beam breaks 
and the levers descend, the wire is withdrawn from its hole, 
releasing the cutoff, which in turn is drawn back by the spring 
cutting off the supply of sand. The weight of the sand in the 
lower can is determined and multiplied by ten. This product 
will give the load which caused the specimen to fail. 

IV. Walk and Floor Work 

1. Class-room Work. 

(a) Equipment for concreting. 

Reference : 

" Lessons in Concrete," No. 8. 

General Notes: 

The equipment necessary is as follows: Mixing platform, 
measuring box, screen, trowels, straightedge, tamper, float ? 
wheelbarrow, water barrel, shovels, and pails. 

(b) Forms for flat concrete work, sidewalk, and floor slabs. 

78 



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References : 

Published lectures: " Concrete Walks, Floors and Pave- 
ments." 
Bulletin No. 26, " Concrete in the Country," pp. 28-34 inc. 

General Notes: 

See accompanying Plate No. 9 showing one-course and two- 
course walks and the tools used in constructing them. 

(c) Concrete walk and floor construction. 

Reference : 

Bulletin No. 26, " Concrete in the Country." 

" Lessons in Concrete," No. 6. " Concrete Surfaces." 

2. Form Work. 

(a) Construction of forms for any of the following: Sidewalks, horse 

blocks, curbs, dairy barn floor, monolithic steps. 

(b) Exercise in finishing concrete surfaces with wood and steel 
trowels, noting the effect of excessive troweling with steel 
trowel, which brings the cement and finer particles to the sur- 
face. 

Exercise 3 
Form for Concrete Horseblock 

(Plate No. 7) 

Tools necessary for constructing the form: Saw, plane, try 
square, gauge, hammer. 

BILL OF MATERIAL 

2 pieces 2 inches x 10 inches x 33^ feet 
1 piece 2 inches x 10 inches x 2]4, feet 

1 piece 2 inches x 10 inches x 2 feet 8 inches 

2 pieces 2 inches x 8 inches x 23^ feet 
2 pieces 2 inches x 8 inches x 2 feet 

Before assembling the mold, each piece should be oiled thor- 
oughly on both sides with linseed oil, as well as on the ends. 
This will also prevent any tendency of the mold to warp or 
buckle. 

Exercise 4 - 
Concrete Porch and Step Construction 

(Plate No. 8) 

Tools necessary for constructing the form: Saw, square, ham- 
mer. 

The accompanying plate is self-explanatory. The same pre- 
cautions should be taken as described in connection with all 
wooden forms as to selection of lumber and oiling, so that the 
form can be removed easily. It is possible to construct the 
form using stock lengths, and the plank can again be used for 
other forms. 

82 




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Exercise 5 
Details of Cement Sidewalk Construction 
(Plate No. 9) 
Tools necessary for constructing form : Ax, saw, hammer. 
2 by 4 or 2 by 6 inch lumber should be used for the forms, 
except for curves, where common house siding or other thin 
lumber (or sheet metal) will be found convenient. 
Forms of 2 by 4 inch stuff should be used for a walk 4 inches 
thick and 2 by 5 inches for walks 5 inches thick. 
3. Concrete Work. 

Construction of horseblock; steps, sidewalk. 

V. Elementary Theory of Reinforcement 

1. Class-room Work. 

(a) Definition of tension and compression. 

References : 

"Concrete Plain and Reinforced," Taylor and Thompson. 
" Reinforced Concrete Construction," Vol. I, Geo. S. Hool. 
Published by McGraw Hill Publishing Company, New York 
City. 

General Notes: 

Concrete is a material which is strong in compression, or 
crushing strength, but, like other masonry, is weak in resist- 
ing tension or pulling force; therefore it must be reinforced 
with steel, which is strong in tension. 

(b) Reinforcing materials. 

References : 

"Concrete Plain and Reinforced," Taylor and Thompson. 
"Reinforced Concrete Construction," Geo. S. Hool. 

General Notes: 

Suitable materials: Steel rods — round, square, and twisted 
square, or of special section, providing they have a sufficient 
cross-sectional area. Woven- wire fabric especially made for 
reinforcing, wire cables, and similar reinforcing are used ex- 
tensively. 

(c) Most efficient placing of reinforcement in simple exercises. 

General Notes: 

Care must be taken to place the steel reinforcing where it will 
do the most good, and this, of course, will depend upon the 
loads, point of application, etc. For instance, a fence post 
will be subject to different stresses and strains than would a 
beam supported at both ends with the load applied trans- 
versely; and a slab in a vertical position, as in a wall, will be 
subject to different strains than one in a horizontal position. 
A few blackboard sketches will help bring out some of the 
elementary principles of reinforcing. 

85 



VI. Unit Construction 

1. Class-room Work. 

(a) Forms for unit work; reinforcing; assembling. 

References : 

" Reinforced Concrete Construction," Vol. II, G. S. Hool. • 

General Notes: 

Often, in the use of concrete in building construction, various 
parts of the structure are cast as units, such as wall sections, 
posts and columns, and when properly hardened are as- 
sembled to form the structure. 

(b) Designing pedestals, sun-dials, garden-seats, plates for baseball 

diamonds, and other unit exercises mentioned on page 66. 
References : 

See plates Nos. 10 and 11. 

General Notes: " 

There are many small articles that can be designed by the 
student, such as foot-scraper, door-weight, small tile, home- 
plate for baseball diamond, etc. 

2. Concrete Work. 

(a) Construction of unit dog-house; a flight of unit steps; pedestal; 
garden-seat, etc. 

Exercise 6 
Lawn Pedestal 

(Plate No. 10) - 

There are three simple designs shown on the plate which lend 
themselves nicely to the material. Forms in which to cast 
them are easily constructed. 

A 1 : 2 mixture of cement and sand is to be recommended, though 
in some cases a 1:3 mixtures might be found satisfactory. 
Various surface effects can be secured by using marble or gran- 
ite screenings, ground mica, or combinations of two or more 
different aggregates. A little experimenting with available 
aggregates will soon show the variations in color possible with- 
out resorting to the use of artificial coloring. (Under the head- 
ing Colored Surfaces, additional information is given on this 
subject.) Scrubbing the surface of green concrete in which 
variegated colored aggregates have been used will result in 
decidedly pleasing effects. 

Exercise 7 

Garden Bench 

(Plate No 12) 

The plate shows plainly the construction of the forms and 
the method of reinforcing. 

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The concrete mixture should be composed of 1 part Portland 
cement, 2 parts of clean sand, and 2 parts of crushed stone or 
gravel, ranging in size from }/± inch to Y2 inch. If, however, 
no coarse aggregate is used, a 1 : 2^ or a 1 : 3 mixture of cement 
and coarse sand should be used. 

The slab and pedestals are cast separately. In making the 
slab, first fill the mold uniformly to a depth of % inch and then 
lay the reinforcing as indicated on the plate, having pre- 
viously laid out and wired together at intersections the rein- 
forcing to correspond with the dotted lines on the plate. 
On top of this place the remaining 2^ inches of concrete, which 
should be wet enough to require only slight tamping to flush 
water to the surface. Following this the mold may be shaken 
to cause the concrete to settle into corners. This top surface 
will be the top of the finished bench, therefore it will pay to 
use care in finishing it to as smooth a surface as possible. An 
edger is run around the inside of the form to give a rounded 
edge to the top of the slab. 

General Notes: 

Do not attempt to remove the form from the under side of 
slab for at least seven days; under favorable conditions, the 
sides of the form can be removed after forty-eight hours. 

VII. Posts and Columns 

1. Class-room Work. 

(a) Concrete fence-post construction. Hitching posts; ornamental 

posts and columns. 
References : 

" Lessons in Concrete," No. 7. 

United States Department of Agriculture Farmers' Bulle- 
tin No. 403. 

General Notes: 

Concrete posts have been constructed in a great variety of 
shapes — triangular, round, square, half-round, etc. The 
rectangular post commonly used by farmers is 7 feet long, 
5 by 5 inches at the bottom, and tapers to 3 by 3 inches at the 
top. The length, 7 feet, permits placing 2J^ feet of the post 
in the ground. Some prefer an 8-foot post. 

(b) Corner and gate-posts; size and bracing. 

References : 

Same as under (a). 

General Notes: 

Concrete corner, end, and gate-posts should be square, and 
the sides should be not less than 12 inches wide, and the post 
should be placed from 3 feet 6 inches to 4 feet in the ground. 

2. Form Work. 

(a) Construction of forms for fence line posts (two designs) ; corner 

90 



and gate-posts (two designs); hitching-posts and lighting 
standards. 
3. Concrete Work. 

(a) Construction of forms for line posts ; concrete base for steel and 
wooden posts; gate-posts; hitching-posts; lighting standards. 

VIII. Foundations and Piers 

1. Class-room Work. 

(a) Laying out, and excavating for, foundations. 

References : 

"Lessons in Concrete," No. 5. 

Bulletin No. 26, " Concrete in the Country." 

General Notes: 

In preparing to erect any rectangular structure a base line 
should first be established, and from it the several corners be 
located by accurate measurement at right angles, and then 
all measurements should be checked back to the base line. 
The depth of the excavation depends upon the height and 
character of the building, but should always go to solid earth 
and below frost line. 

(b) Forms for mass construction. 

References : 

Same as those under (a). 

General Notes : 

Forms for piers and machinery foundations are constructed 
in substantially the same manner as are forms for regular 
building foundations. 

(c) Repairing old barn foundations. 

References : 

See those under (a). 

General Notes: 

Foundations which are laid up in mortar may disintegrate 
and crumble, and this condition frequently exists in buildings 
which are otherwise in a fair state of preservation and well 
worth saving. If the foundation wall has not gone to pieces, 
a large portion of it can often be left in position and boxed in 
with concrete. If that part of the foundation below ground 
is left in good condition, it may be capped with concrete. It 
will, of course, be necessary to take the load of the building 
off the foundation temporarily, so that the crumbled portions 
may be removed and the new concrete be given a chance to 
harden. It may also be necessary to replace old sills and 
splice posts. 

2. Form Work. 

(a) Forms for foundations (three types). 

(b) Forms for piers. 

91 



Reference : 

Bulletin No. 26, " Concrete in the Country." 
3. Concrete Work. 

(a) Construction of a section of foundation wall by the students. 
{Note. — The students will take a greater interest in the work if 
it is possible to go out and do a little practical concreting around 
the school grounds or in the vicinity, such as building or repair- 
ing a piece of sidewalk, foundation wall, etc.) 

IX. Ornamental Work 

1. Class-room Work. 

(a) Core making; shaping of reinforcement; the use of clay molds; 
plaster and glue molds and cores; coloring and finishing sur- 
faces. 

References : 

Ralph Davison!s book, " Concrete Pottery and Garden Furni- 
ture." 
" Lessons in Concrete," No. 6, The Surface Finish of Concrete. 

General Notes : 

In case ornamental work is to be attempted, Ralph Davi- 
son's book should be obtained. This book takes up the sub- 
jects of plaster molds, glue molds, and wire forming in a 
simple manner. 

Colored Surfaces 

For artistic work it is better to depend upon selection and combination 
of aggregates of various colors than upon any process of coloring by pig- 
ments. However, artificial coloring-matter, if used, should never exceed 
8 per cent, of the weight of the cement, and should be mixed with dry cement 
before water is added. Nothing but mineral coloring-matter should be 
used, and the following table, taken from " Cement and Concrete," by L. C. 
Sabin, is generally accepted as the standard authority for amounts of dif- 
ferent coloring materials required to produce certain shades: 

COLORED MORTARS 
Colors Given to Portland Cement Mortars Containing Two Parts River Sand 

to One Cement 



Dry material 


Weight of Coloring-matter Per Bag of Cement 


used 


K pound 


1 pound 


2 pounds 


4 pounds 


Lamp-black 

Prussian blue 

Ultramarine blue . . 

Yellow ocher 

Burnt umber 

Venetian red 

Chattanooga iron 

ore 

Red iron ore 


Light slate. 
Light green slate. 

Light green. 
Light pinkish slate. 

Slate, pink tinge. 

Light pinkish slate. 
Pinkish slate. 


Light gray. 
Light blue slate. 
Light blue slate. 

Pinkish slate. 

Bright pinkish 
slate. 

Dull pink. 
Dull pink. 


Blue gray. 
Blue slate. 
Blue slate. 

Dull lavender 

pink. 
Light dull pink. 

Light terra-cotta. 
Terra-cotta. 


Dark-blue slate. 
Bright blue slate. 
Bright blue slate. 
Light buff. 
Chocolate. 

Dull pink. 

Light brick red. 
Light brick. 



92 



2. Form Work. . 

(a) Construction of ornamental molds and cores for flower-boxes, 
straight line vases, round fern jars, circular vases, with and 
without a handle, urns, drinking fountains, bird baths, animal 
drinking tanks, etc. 

3. Concrete Work. 

(a) Construction of exercises selected from above. (Note. — By 
this time the students should be sufficiently familiar with the 
work to plan original exercises of their own. The instructor 
should encourage originality, and also give the students oppor- 
tunity to make some preferred exercise.) 

Exercise 8 
The Construction of a Concrete Flower-box 

(Plate No. 14) 

The long window-box shown in Plate No. 14 should be made 
of 1 part cement and two parts of clean sand, and will take 
approximately 32 pounds of cement and % cubic foot of sand. 
The student should have little trouble in making the form if 
the directions shown on the plates are closely followed. 

After the surfaces of the form that are to come in contact with 
the concrete have been well oiled, the form should be assembled. 
Reinforcing should consist of 3^-inch galvanized square-mesh 
wire, which is placed in position by making a basket that, 
when put in place in the form, will be Y2 m °h from the inside 
surface of the form. This basket can be held in place by slip- 
ping blocks between it and the inside form, these to be removed 
after the concrete has been deposited up to within about three 
inches of the top of form. 

Sand should be measured out accurately and placed upon the 
mixing board in a thin layer. The cement is then distributed 
over the sand and the two are mixed until the color is uniform. 
Water should be added slowly from a sprinkling can until the 
mixture is thin enough so that it will flow readily into and fill 
all parts of the form. A trowel, or a thin, flat stick with a 
chisel end, should be worked up and down along the inside of 
the form so as to force the coarse particles of the mixture away 
from the surface. 

It is not advisable to remove forms until the flower-box has 
been in the mold for at least twenty-four hours, and a great deal 
of care should be taken when removing the form so as not to 
damage the green concrete. After removing the form the out- 
side surface should be brushed with a stiff brush or an old 
broom; the flower-box should then be allowed to air-dry pos- 
sibly two or three hours, but be kept from drying out too rap- 
idly; never place in the sunlight. The box should then be 
placed in water and allowed to soak for three or four days. A 

93 



very smooth surface can be obtained by sprinkling dry cement 
over the wet surface after removing from the water and rubbing 
the cement in with a scrubbing-brush or with a block of cork. 

(The above directions will also apply in constructing the smaller 
flower-box on Plate No. 14.) 



94 




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